In 2019, Old Easton Road Bridge in Plumstead Township had to be replaced. Its past several inspections showed increasing scour issues and deterioration of the main load-carrying members, indicating it was becoming structurally deficient.
The township wanted to replace the original two-lane bridge with a more robust design, but they were limited by permit requirements and other restrictions that prevented widening the roadway. The township also had a limited budget, which further constrained the design team, says William Castle, founder and president of W.J. Castle, P.E. & Associates.
“The biggest challenge was to design the bridge within the township’s limited budget and timeframe,” Castle says. “This included construction considerations, such as maintaining the existing under-clearance, and saving what we could on the old bridge, while ensuring the design was able to handle the required load ratings.”
The original bridge was a single span concrete T beam structure founded on stone masonry abutments. The age, foundation type, and bottom of footing elevations were unknown, and no original drawings or records of the bridge were available.
It left many questions unanswered, but Castle had worked with precast concrete on many previous projects and he knew it would help his team to address all of these challenges.
A 1700s Look in a Modern Design
The design team came up with a solution that allowed the new bridge to remain in the exact footprint of the previous structure and to blend seamlessly with the surroundings. It included tinted stone facing on the fascia and wingwalls, precast concrete box beams, and painted bridge railings, to make the new bridge feel like it had been there for centuries.
“They gave extensive thought and care to the character of the area with a 1700s-era mill that is now an elegant restaurant in the shadow of the bridge,” says Alan Bleam, director of the Plumstead Township Public Works.
The existing stone abutments and wingwalls were left in place with the top portion removed. New abutments were installed behind the existing abutments to support the adjacent precast concrete box-beam superstructure. To accommodate the existing gas main and leave room for future utilities, two open bays were incorporated in the design. Reinforced concrete moment slabs were installed on top of the partially cut wingwalls, and stone facing was then added to the parapets and exterior face of the bridge to create the desired aesthetic.
This approach reduced the earthwork required, which made permitting easier to obtain, and preserved the existing hydraulic opening. The remaining stone abutments and wingwalls now act as scour protection for the new bridge.
“The design provided cost and time savings to the residents of Plumstead by allowing us to forego the need for PA DEP [Pennsylvania Department of Environmental Protection] permits to work in the waters of the commonwealth,” Bleam says. “This was [achieved] by designing and installing the new bridge abutments ‘behind’ the existing ones.”
“The prestressed concrete beams were also easy to fabricate and easy to install,” adds Castle. He notes that all seven box beams were installed over two working days. “This reduced labor costs and construction time.”
The project was successfully completed in July 2020, ahead of schedule and on budget, thanks to the innovative design strategies and thoughtful implementation of precast concrete, Castle concludes. “The client is extremely happy that the township now has a new bridge that is going to last for many years.”