Design and construction of fatigue-prone detail retrofits for Interstate 79 Neville Island interchange bridges

Abstract

The Interstate 79 Neville Island Interchange Bridge complex located north of Pittsburgh, Pennsylvania, carries four through lanes of the Interstate over Neville Island and the main and back channels of the Ohio River. The mainline bridge consists of a tied through arch span and 26 dual parallel approach spans. These mainline dual approach spans are continuous units comprised two welded steel plate deck girders, welded steel plate floorbeams and rolled steel wide-flange stringers. In addition, the complex includes eight ramp bridges consisting of both straight and curved continuous dual welded steel plate girders, welded steel plate or rolled wide-flange floorbeams and rolled steel wide-flange stringers. These structures, built and opened to traffic during the early to mid-1970s, are owned and maintained by District 11-0 of the Pennsylvania Department of Transportation. All nine bridges are considered fracture-critical (FCM) owing to the two-girder floorbeam system used on the mainline approach spans and all of the ramp bridges. The steel welded box tie-girder of the main tied-arch span also makes this span fracture-critical. SAI Consulting Engineers, Inc. has performed the required annual NBIS and FCM inspections for the last15 years on most of these structures. There were many brittle fracture and fatigue-prone details that were of concern; some of which were cracked. These details included girder-floorbeam and stringer-diaphragm out-of-plane distortion, floorbeam flange end terminations, floorbeam-to-girder welded kneebrace connections, poor weld details at back-up bar splices, intersecting welds of transverse and longitudinal stiffeners, etc. In 2000 and 2005, SAI developed fatigue retrofits for nine brittle fracture or fatigue sensitive-type details that were part of two major design rehabilitation contracts. In 2003, SAI also designed retrofit-type repairs for an emergency contract to retrofit existing Hoan-like details. This paper discusses the design, fabrication, and construction of the retrofits for these various brittle fracture and fatigue-prone details.