SR 209 East Broad Street Bridge
The East Broad Street Bridge, an 1890’s era stone masonry-arch structure with retrofitted steel sidewalk supports, was designated to be rehabilitated or replaced mainly due to the condition of the sidewalks. The stone arch core was not only worth rehabilitating but also was a contributing element to both national and local historic districts. Working with the local historic commission, the designers chose haunched precast concrete beams for the new sidewalk structure.
The Historical and Architectural Review Commission preferred a concrete structure, and designers saw the project as an opportunity to expose and reintroduce the original arch bridge to visibility. The precast concrete system was chosen for four reasons, according to Paul J. Rea, senior associate with Ammann & Whitney, the structural engineer.
“Precast concrete’s clean appearance and earthy tones would look natural when placed next to the original stone masonry,” he explains. It also created arched, variable-depth beam shapes that complemented the adjacent stone arches beams in an economical way while exposing as much of the original historic arch as possible. The precast design provided the flexibility to modify the beams as necessary and offered the capability to get continuous action for live loads and superimposed dead loads while allowing shorter beams. That facilitated delivery and erection in a tight urban setting.
Since rehabilitating the stone masonry arch took considerable time, the precaster had more than enough time to cast the prestressed beams and ensure they were ready when the arch rehab was completed. “Once the prestressed beams were set in place, the project advanced quickly to substantial completion.”
One innovative feature involved passing the prestressed concrete beams over the dry-stack retaining walls and supporting them on a solid, integral abutment while creating a faux concrete seat and end diaphragm at the wall. This made it appear that the beams were supported there as part of the wall. “The members of the HARC and the Museum Commission really loved this approach, since it looks historic while meeting current design standards.”
The result is a typical prestressed concrete bridge with modified elements that created a distinctive design worthy of being placed next to a historic stone arch. “This solution was mainly about being creative within the rules,” he says.
Consultant Project Manager:
Structural Precast Elements:
• 12 14-inch-wide solid haunched prestressed concrete beams (four per span).
• Beam depths varied from 18 inches to 36 inches at the supports.
• Beam lengths varied from 40.3 feet to 35.9 feet.
• Eight precast concrete capstones on each concrete pilaster.