For Immediate Release
Engineering Analysis: Moisture in Wooden Beam Caused Kearney Bridge Failure
A forensic engineering analysis by engineers from the City of Springfield’s Department of Public Works, the Missouri Department of Transportation and private engineering consultants has determined the cause of the structural failure of the pedestrian bridge on West Kearney Street in early November.
Moisture infiltration over the 30-year life of the bridge caused one of the bridge’s two wooden beams to sag, which in turn caused the deck above to shift. The analysis confirmed that at no point was the bridge in danger of collapse from structural failure, or an endangerment to people or property.
Based on visual inspection and information available at the time, a bearing failure — not the wood beam — looked like a potential culprit. Because engineers take all unexplained movements in stationary structures very seriously, the Department of Public Works chose to take no chances in deciding to conduct an emergency removal of the bridge on Nov. 3. The forensic analysis later revealed no issues with the bearings. However, the analysis also determined the bridge was non-repairable, and would have had to be removed anyway.
Compounding the situation was a design that prevented engineers from fully viewing and inspecting the structure while the bridge was in place. The beam at issue was located below the concrete walking surface. Following their analysis, the engineers agreed that this area, by its very construction, was neither visible nor maintainable. Their findings led the committee to recommend that pedestrian bridges built in Springfield in the future use steel beams rather than laminated wood beams. None of the other five pedestrian bridges in Springfield use wood beams — all are constructed with steel.
Representatives from the City and Springfield Public Schools agree that a pedestrian bridge is needed in this location, and MoDOT has expressed support for this conclusion.
The City’s goal is to complete construction of a new bridge before the school year begins in August 2011. Funding for a new bridge is likely to come from the City of Springfield’s 1/8-cent Transportation Sales Tax. The project would easily fall within the bounds of the stated use for this tax. Preliminary cost estimates for a replacement bridge range from $1 million to $1.5 million, depending upon design specifications and right-of-way requirements. A new bridge must conform to standards outlined in the Americans with Disabilities Act, which will likely change the necessary footprint of ramps on either side of the roadway.
Public Works is also working with Williams Elementary teachers and administration to involve the students in the new bridge process in some way, including potential educational opportunities and a possible contest to name the new bridge or choose a cosmetic design element.
For more information, contact: Phil Broyles, Co-Interim Director of Public Works, (417) 864-1950.
Download the Kearney Walkbridge Report (PDF)