Sources: Northeast Prestressed Products, Cressona, Pa.; PCI Mid-Atlantic, Lancaster, Pa.; CP staff
The Coplay-Northampton Bridge, linking Pennsylvania’s Lehigh and Northampton counties, marks the U.S. debut of Electrically Isolated Tendons (EIT)—part of a reinforcement scheme in 25 of 52 bulb-tee girders that Northeast Prestressed Products is fabricating for the 1,124-ft. Lehigh River crossing. Proven in Europe and advanced here by the Federal Highway Administration, EIT allow for verification that post-tensioning cables have been encapsulated per specifications, and provide enhanced durability and non-destructive condition assessment over time.
The process uses a tight polymer duct that encapsulates high-strength steel and grout, creating a protective alkaline environment for strands plus an anchor head isolated from the ground and companion reinforcement. Electrically isolated anchorages allow a bridge owner to a) check plastic duct integrity during and after construction; and, b) use electrical impedance measurements to monitor corrosion protection of the high-strength steel throughout a structure’s service life. EIT adoption requires minimal changes to present North American precast/prestressed concrete bridge practice.
Scheduled for opening in 2020, the new Coplay-Northampton Bridge, or Chestnut Street Bridge, will succeed a 1930s crossing. The replacement structure will be a three-span continuous bridge with four spliced bulb tees. Five girder lines will be post-tensioned and grouted with four tendons per line. A composite cast-in-place concrete deck will complete the structure. In addition to the tendon specification, the Chestnut Street Bridge becomes the first Keystone State crossing to utilize prestressed and post-tensioned bulb tee beam construction, including spliced girders.
The FHWA had been searching for a project to demonstrate EIT, and pegged the Lehigh-Northampton project after conferring with Lehigh County and the Pennsylvania Department of Transportation on schedule, time and costs. Joining the agencies in tendon demonstration are post-tensioning strand provider Dywidag Systems International and Lehigh University, representatives of which will monitor near- and long-term tendon confinement.
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