A Faster, Cheaper Way of Repairing Steel BridgesJohn Simpson | August 30, 2016
The American Association of State Highway and Transportation Officials estimates that it would cost roughly $48 billion to fix the 72,868 structurally deficient bridges in the United States. Compounding the high cost of repair are the lengthy delays and disruptions to traffic associated with such maintenance.
Engineers from the University of Connecticut have now devised a method for quick and enduring repairs to many such bridges that may also reduce the expense of these projects. Researchers led by Arash Esmaili Zaghi, assistant professor in the university's Department of Civil and Environmental Engineering, have proposed using ultra-high performance concrete (UHPC) encasings to retrofit the corroded ends of steel bridge girders—one of the most prevalent deficiencies in steel bridges.
UHPC is a low-porosity, cement-based, fiber-reinforced composite with compressive strengths in excess of 22 ksi and excellent durability properties. The repair method involves casting thin UHPC panels on each side of the girder web. Shear studs welded to undamaged portions of the web and flange engage the UHPC panels and provide an alternate load path.
The researchers postulated that this repair method would be superior to the current practice of attaching steel cover plates for several reasons:
· Paint removal and surface preparation are not required for this rehabilitation method, as high-strength concrete may be cast over painted surfaces.
· The rehabilitation can be applied under in-situ stress conditions, i.e., the bridge doesn't need to be jacked up before repairs can be carried out on the support structure.
· UHPC is self-consolidating and pumpable, making it ideal for application in the complex geometries and tight spaces common around bridge bearings and diaphragms.
· Concrete panels may protect the original steel from further corrosion.
A proof-of-concept project was conducted to demonstrate the effectiveness of UHPC encasement to rehabilitate corrosion damage in steel girder ends. The project emphasized investigating the load-bearing capacity of a damaged girder to potentially restore its capacity using this repair technique.
The researchers found that the bearing capacity of the repaired girder exceeded that of an undamaged girder by approximately 25%. The repair prevented the failure of the girder at the bearing. Only very fine cracks formed on the UHPC panels, and the beam began experiencing extensive flexural yielding.