Wyoming bridge inspections under way
August 7, 2007
Two Wyoming bridges that share the same type of design as the failed bridge in Minneapolis, and a third bridge with a similar design, will be inspected in the coming week as a safety precaution, according to the Wyoming Department of Transportation (WYDOT).
WYDOT bridge inspectors began looking at the US 26-89 bridge over the Snake River at Hoback Junction south of Jackson today (Tuesday, August 7). That bridge is a deck truss arch structure, a design similar to the Interstate 35W bridge that collapsed in Minneapolis on August 1st.
The Snake River bridge inspection is expected to take two days to complete, after which the inspectors will move on to the Fremont County Road No. 298 bridge over the Wyoming Canal near Diversion Dam Junction. That bridge is about 40 miles northwest of Riverton. It is one of 756 bridges around the country the Federal Highway Administration has identified as sharing the steel deck truss design of the Minneapolis bridge.
Once that inspection is completed, the inspectors are expected to begin early next week on the I-25 service road bridge over the South Fork of the Powder River south of Kaycee. That is a steel deck truss bridge maintained by WYDOT.
U.S. Secretary of Transportation Mary Peters called on states to inspect any bridges of a similar design to the one that collapsed in Minneapolis. "Even though we don't know what caused this collapse, we want states to immediately and thoroughly examine all similar spans out of an abundance of caution," Peters said.
Safety is WYDOT's top priority, and every bridge in the state is inspected at least once every two years, and more frequently if needed. The department has been using a robust bridge inspection program for many years to effectively prioritize bridge rehabilitation and replacement projects.
The inspections measure and record required National Bridge Inventory items including dimensions, clearances, alignments, waterway data and structural condition. The structural condition is evaluated using structural elements such as girders, decks, railings, columns and pilings. Each element is evaluated based on several condition state assessments.
"We're confident WYDOT's bridges are safe, but we're happy to comply with the U.S. DOT's request and have already scheduled re-inspections of the three bridges in question," said Keith Fulton, WYDOT's assistant state bridge engineer.
WYDOT tracks the status of 2,774 bridges around the state utilizing a bridge management system. Of that total, 1,929 of the bridges are owned and maintained by WYDOT, and 845 are under the jurisdiction of municipalities and counties.
"Our inspections are based on a variety of factors which may result in a bridge being rated as structurally deficient or functionally obsolete, but that does not mean that bridge is unsafe. It just means it may need repair or possibly replacement," Fulton said.
Among the WYDOT-owned bridges, 1,838 (95 percent of the total) are classified as acceptable, with the remaining 91 being structurally deficient or functionally obsolete. Among city- and county-owned bridges, 597 (71 percent) are acceptable and 248 are structurally deficient or functionally obsolete.
When all state- and locally-owned bridges are combined, 88 percent of the 2,774 bridges are classified as acceptable, and 12 percent are classified as structurally deficient or functionally obsolete.
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 unsafe or likely to collapse. If inspectors find unsafe conditions they will restrict access or close the bridge.
Structural deficiency or functional obsolescence are classifications used to determine eligibility for federal bridge funds rather than as an indication of safety, and they are determined by the Federal Highway Administration.
Structural deficiency is determined by an assessment of physical condition and load ratings.
Physical condition assessments are made by inspectors who look for deterioration of bridge elements which include the deck, girders and supporting columns. Deterioration could include rusting of steel components, cracking of concrete, or something as simple as peeling paint. Load ratings refer to how much weight the bridge can carry on a repeated basis, without damaging the structure.
Functional obsolescence is judged by how well the bridge meets current and anticipated traffic volumes and types, and whether it has enough travel lanes and sufficient clearance.
Information based on a WYDOT media release