Fairmount Line Bridges Reconstruction
In 2010, officials from the Massachusetts Bay Transportation Authority determined that the two bridges carrying commuter rail over the bucolic Neponset River had reached the end of their fatigue service life. Both bridges were more than 100 years old, and both were deemed structurally deficient with fatigue ratings below the statutory limits.
Best Solution – Precast Concrete Bulb-tee Beam Design
The best solution to meet all of those needs was a long-span precast concrete bulb-tee beam design. “The prestressed, precast concrete bulb-tee beam bridge proved to be the most economical design solution to meet the project requirements and accommodate all construction constraints that this bridge replacement project encountered,” stated the project engineer.
The bulb-tee beam optimized the strength-to-weight ratio to maximize the carrying capacity for live loads. At the same time, the wide top flange of bulb-tee beam eliminated the need for formwork for the bridge deck.
Shorter Construction Duration
The team was able to shorten construction duration by constructing the concrete deck right after the erection of the beams. The use of precast concrete beam with ballasted deck in this application also prevented construction debris from falling into the river, improving environmental sustainability and safety for the recreational users along the river.
Thanks to the phased construction using a long-span precast concrete beam, the project was completed six months ahead of schedule and under budget without any change orders. “The precast concrete design utilized the advantage of prestressed concrete beams for cost effectiveness, maintenance-free operation, and aesthetic appearance to extend service life for the bridges,” Alzaim says.
Versatility of Precast Concrete
The project was a great success and a testament to the versatility of precast concrete, says Troy Jenkins, chief engineer at Northeast Prestressed Products in Cressona, PA. “We were able to build prestressed beams for a bridge that typically would have only considered a steel bridge design,” he says. “That’s the main thing we love about this project.”
All the precast components were manufactured by Northeast Prestressed Products LLC, Cressona, PA.