I predict in the future this technology should be considered for every pre-stressed and post-tensioned project.
LANCASTER, Pa. (PRWEB) July 11, 2019
Northeast Prestressed Products (NPP), a PCI Mid-Atlantic Producer Member and manufacturer of prestressed/precast products for the Mid-Atlantic, New England and surrounding areas, has a key role in a prominent Lehigh Valley bridge replacement project that is currently underway.
Lehigh and Northampton Counties are replacing their 1930’s era bridge over the Lehigh River with a durable precast prestressed concrete structure. The Coplay-Northampton Bridge replacement has a $33.5 million price tag and will connect the two boroughs for motorists and pedestrians.
This project is the first in Pennsylvania to utilize pre-stressed and post-tensioned bulb tee beam construction including spliced girders, and the first in the U.S. to use Electrically Isolated Tendons (EIT).
The replacement structure will be a three-span continuous bridge using pre-stressed bulb tee girders, with four splices along the span. The 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.
The bridge is one of the most heavily traveled in the Lehigh Valley, and so many people walk the bridge every day that the county is providing a shuttle bus six days a week for the duration of the project.
AECOM is the architect and structural engineer for the bridge project. Jason Beecher, PE, AECOM Project Manager, recalls that the company has been working on this project for more than a decade.
Their memorandum of agreement with Lehigh County included architectural features on the replacement structure like ornamental lighting and reconstruction of the tow path to service the old canal.
All interested parties were eventually satisfied, and the project moved forward.
“AECOM was selected back in 2004 as the A and E for this design/bid/build project. We worked with the community to develop a durable structure for Lehigh County,” explained Beecher.
AECOM had to overcome community sentiment for the older structure by performing public outreach. The resulting concrete structure accommodates the addition of a turn lane as well as improving the durability and under-clearance.
“The AECOM team was able to keep the existing pier locations in the river and through substructure evaluation determined they were adequate to support the new loading. We didn’t have to put in coffer dams, and we minimized disruption to the fish migration seasons,” recalls Beecher.
The use of the pre-stressed post-tensioned spliced girders was selected back in the TSL stage, but it wasn’t until the design development stage that the Federal Highway Administration (FHWA) showed interest in the project to test a new method of corrosion protection.
IT’S GOOD TO BE FIRST
The bridge replacement project is the first in Pennsylvania to utilize pre-stressed and post-tensioned bulb tee beam construction including the spliced girders. And it’s the first project in the United States to use Electrically Isolated Tendons (EIT), a technology that is readily available and has been successfully used in Europe.
The EITs allow for verification that the post-tensioned cables have been encapsulated, as per the plans and specs, while they provide enhanced durability and non-destructive condition assessment over time. It requires minimal changes to current construction practices and provides an incentive to improve workmanship.
“The use of the demo EIT technology did not have an adverse effect on the project schedule or budget,” explains Larry Franko, Project Manager with Pennoni Associates.
“I predict in the future this technology should be considered for every pre-stressed and post-tensioned project,” adds Franko.
The EIT process uses a tight polymer duct that encapsulates the high-strength steel along with grouting that creates a protective alkaline environment for the steel strands and an anchor head that is isolated from the ground and the normal reinforcement of the structure.
The use of electrically isolated anchorages allows the team to check the integrity of the plastic duct during and after construction and to monitor the corrosion protection of the high-strength steel during the whole service life with electrical impedance measurements.
The FHWA had been searching for a project that fit the criteria to demonstrate the EIT system. In conjunction with Lehigh County and PennDOT, the Coplay bridge project was selected after vetting concerns about schedule, time and cost.
Lehigh University and Dywidag Systems International (DSI) also played a part in this groundbreaking project.
The engineering and transportation divisions of NPP worked with Trumbull, project contractor, to overcome challenges in the development and delivery of the beams. Beam delivery met several snags as the travel route had to be adjusted so the prestressed concrete beams – the longest at 139’4” – could be backed down a narrow street to access the crane.
According to Franko, only one route was deemed acceptable for the delivery of the prestressed beams. Unbeknownst to the team, a local township construction project impacted that route.
“There was no other way to reach the staging area and we were looking at a possible 6-week delay,” says Franko. The team devised a way to use a local street within the detour in conjunction with a public parking lot. That creative solution avoided major delays.
Mother Nature poured buckets of rain on Pennsylvania in 2018. It was one of the wettest years on record, with the Lehigh Valley receiving more than 20” of rain above normal, putting a damper on the construction schedule.
“The causeways were frequently submerged due to the rain,” says Beecher. “Since they were needed to erect the pre-stressed beams, we had to increase the elevation to make sure they weren’t washed out.”
The temporary causeway was designed based on the driest month of August, but the causeway was flooded because of the extremely rainy summer, so a concrete foundation was installed to support the temporary towers.
Another challenge for the team was performing a full-scale mockup of the post-tensioning operation. Franko recalls it wasn’t easy finding a level space 600 feet in length where they could mimic the exact bridge profile. Trumbull found space that allowed the interested parties to walk through the process and satisfy PennDOT and FHWA.
As with any spliced girder project, there were some challenges.
“There was some difficulty with alignment and movement with the drop in sections between the 2 haunched girders on opposing piers that were held in place only by the use of strong backs. The section between the piers was the farthest reach and that piece was difficult to maneuver. In order to avoid the PT ducts, we had to drop it down alongside and move it laterally into place,” says Franko.
There was a slight misalignment of the PT ducts due to the temporary forces on each end of the beams. They came up with a scheme to jack the beams which allowed everything to be moved within allowable tolerances.
Lehigh University and DSI will continue to monitor the bridge project and publish the results of their research. The results will confirm how well confined the post-tensioned tendons were during construction. The initial readings were above baseline and from that standpoint the grouting operation was successful.
This non-destructive evaluation method monitors for breeches in the corrosion protection system indicative of the onset of corrosion. In this demonstration project, the emphasis was for the EIT to measure quality control at the time of construction as well as long-term.
As for the project schedule, concrete deck work is scheduled for completion in 2019 with a bridge opening date set for 2020.
- Bridge Description: 3-span continuous bridge, 5 girder lines
- Bridge Length: 1,124 ft.
- Precast Elements: 27 PS Bulb Tee Beams and 25 PS/PT Bulb Tee Segments (spans 4-6) (various sizes)
- Location: Chestnut Street Bridge - Coplay, PA
- Precast: Northeast Prestressed Products, LLC
- Owner: County of Lehigh
- Architect: AECOM
- Structural Engineer: AECOM
- Contractor: Trumbull Corporation
- Construction Manager: Pennoni Associates
- Construction Inspection: Pennoni Associates
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