In 2010, officials from the Massachusetts Bay Transportation Authority determined that the two bridges carrying commuter rail over the Neponset River had reached the end of their service life. Both bridges were more than 100 years old, and both were deemed structurally deficient with fatigue ratings below the statutory limits. They needed to be rebuilt with as little disruption to traffic as possible, which meant any design solution had to accommodate phased construction in an expedited manner under a tight constraint at the bridge site without fouling the adjacent track.
The design team also had to accommodate the requirement to minimize future maintenance costs and eliminate fatigue concerns—all in a cost-efficient package. 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. 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. Overall, the project was a great success and a testament to the versatility of precast concrete.