Published in 2011
As a condition of the Virginia Department of Historic Resources concurring with the decision of the Virginia Department of Transportation to demolish and replace the Advance Mills Bridge in Albemarle County, Virginia, the 2008 “Memorandum of Agreement among the Federal Highway Administration, the Virginia State Historic Preservation Officer, and the Virginia Department of Transportation, Regarding the Route 743 Bridge Replacement in Advance Mills, Albemarle County, Virginia” required that the Virginia Transportation Research Council (now the Virginia Center for Transportation Innovation and Research) conduct a study of the loop-welded (actually forge welded) eyebars prevalent on two pin-connected trusses that were the major spans on the structure. Engineers conducting the required biennial bridge safety inspections of the Advance Mills Bridge for VDOT had reported cracking at the forge line, a flaw frequently found in loop-welded eyebars.
The bridge was included as a contributing structure in the Advance Mills Historic District, which was listed on the National Register of Historic Places and Virginia Landmarks Register. For this reason, the study included a history of the various bridges that served Advance Mills over the years, a history of the community itself, as well as the examination of the loop-welded eyebars.
The researchers anticipated that the examination of the loop-welded eyebars would be limited to an assessment of the adequacy of a “hands on” inspection in disclosing the extent and severity of the cracking at the forge line. Although the hands-on inspection, supplemented by dye penetrant testing, was found sufficient to define the cracking, unanticipated damage during the demolition of the bridge revealed that even hairline cracks or rust stains along the forge lines were indicative of a more serious flaw: a clean separation at the forge line, in no way similar to a conventional welded connection. This separation at the forge lines of the loops was in keeping with warnings in early design texts that the welding of steel was unreliable. Such distress could be critical in an evaluation of the adequacy of a truss if the bridge were to be left in service. This finding is significant because of the nearly 250 extant metal truss bridges in Virginia, 32 are designated as historic (i.e., eligible for or listed on the National Register) and of these, 15 use loop-welded eyebars as do numerous other extant metal truss bridges in Virginia.
This report presents data on the composition and strength of the steel, the effect of the separation on the strength of the eyebar, and findings pertaining to the inspection process and the significance of any cracking that may be found. The study recommends that safety inspections of truss bridges built in the late 19th and early 20th centuries include a careful examination of any loop-welded eyebars and that a hands-on inspection of such eyebars, supplemented by dye penetrant testing, is sufficient to disclose the presence of cracking. Hairline cracks or rust stains along the forge lines should be regarded as evidence of inadequate welds, and appropriate actions should be taken to ensure the safety of the structure. Safety inspectors also should examine portions of the eyebars within the loops for evidence of cracking and those bars obscured by the deck for severe section loss attributable to corrosion. Finally, any pin-connected truss bridges being dismantled should be placed on secure supports after being lifted from their bearings, and during disassembly, the truss should be supported at each panel point to prevent collapse and ensure the safety of workers.
Wallace T. McKeel, Jr., P.E.
Last updated: November 17, 2023