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Field testing and evaluation of the Ironton-Russell truss bridge

2004-12-01
Lenett, Michael
Hunt, Victor
Helmicki, Arthur
Türer, Ahmet
The Ironton-Russell truss bridge spanning the Ohio River between the cities of Ironton, Ohio and Russell, Kentucky was opened to traffic in April 1922. Although this bridge spans the Ohio River between Ohio and Kentucky, it is owned and operated by the state of Ohio and is considered a landmark by both the residents of Ironton and Russell. The main spans of this truss consist of a 3-span cantilever through truss, with a suspended truss in the center span, and a simple span through truss. Visual inspections of these main spans revealed that recent repairs and modifications to various truss members, floorbeams, and stringers utilized weld techniques that violated the ANSI/AASHTO/AWS Bridge Welding Code. Furthermore, these welded repairs reduced the fatigue classification of primary load carrying truss members to Category E and Eí, modified design and construction details used in the original bridge construction, and did very little to contribute to truss member section. When the visual inspection team identified these details as well as section loss at certain truss verticals and diagonals, it was their recommendation to reduce the allowable load on the bridgeís through truss spans from HS14.3 (23.4 tons) to 3 tons. However, enforcing a 3-ton load limit would severely impact the economy of the region ñ the transportation of heavy goods and materials across the bridge would be restricted, thus effecting local industries. Recognizing this, the Ohio Department of Transportation contracted University of Cincinnati researchers to organize and perform field tests on the bridge to provide a better assessment of load capacity and in-situ structural health. As a result, controlled truck-load tests involving high-speed (resistance based) strain gages were performed on the bridge and an instrumented monitor utilizing low-speed (vibrating wire) strain gages was installed at the site. In this manner, both the live load and environmental responses of various instrumented truss members and floorbeams were recorded. The respective data recorded during these field efforts was used not only to evaluate environmental effects on the bridge, but also to compute the load rating for each of the instrumented members. These ratings and their corresponding allowable live loads were subsequently compared to the recommended 3-ton load limit. The results of this comparison, as well as how they were utilized by the Ohio Department of Transportation, are presented within this paper.