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Infrastructure Technology Institute

ITI Presents Results of Live Strain Monitoring of Highway Bridge Bearing Assemblies

In September 2008, members of the ITI Research Engineering Group (REG) attended the American Society for Nondestructive Testing’s “Structural Materials Technology Conference 2008: NDE/NDT for Highways and Bridges” conference in Oakland, California. The conference explored the role of non-destructive evaluation and testing throughout the life cycle of transportation infrastructure. ITI researcher David Kosnik presented “Monitoring of In-Situ Strains in Bearing Assembly Anchor Bolts on a Large Through-Truss Bridge,” which summarized testing and structural health monitoring work done by ITI and University of Kentucky researchers on a major Interstate highway bridge.

The paper covered the response to the failure of an uplift bearing anchor bolt on a the John F. Kennedy Memorial Bridge, a large cantilever truss structure which carries Interstate 65 over the Ohio River at Louisville, Kentucky. Analysis of the failed bolt showed that corrosion fatigue was the likely cause; additional inspections revealed significant corrosion damage to the remaining anchor bolts securing the bearing to the pier. The entire bearing assembly was observed to be moving relative to the pier cap as a result of the reduced restraint. The three remaining anchor bolts and the bearing were instrumented to quantify strains and bearing movement under live traffic.

Similar measurements were performed on the other three uplift bearings on the truss. When the failed anchor bolt was replaced with a threaded rod, the rod was instrumented and tightened to a specified pre-load to secure the bearing. The axial strain was measured by instrumentation as a securing nut was tightened. Changes in strains on the other bearing anchor bolts were simultaneously measured. Dynamic strains in the retrofitted rod and other bearing anchor bolts were monitored under traffic for 17 hours. Continuous remote monitoring of live strains is being employed to evaluate the long-term performance of the temporary retrofit and aid future decision-making.

When not attending conference sessions, ITI personnel staffed an exhibit booth describing ITI’s work to potential deployment partners and others.