By Kevin Wilcox
The Carroll Avenue Bridge in Takoma Park is receiving a structural face-lift for its second 80 years.
The effort to rehabilitate the Carroll Avenue Bridge minimizes the work needed in the sensitive stream and parklands below by reusing the robust foundations and reinforced-concrete arches. © Carletto Aerial Photography
June 14, 2016—Later this month, workers in Takoma Park, Maryland, will carefully begin removing the deteriorated concrete decking, beams, and columns of the Carroll Avenue Bridge, a picturesque concrete tied-arch, open-spandrel span—one of only three in the state's bridge system.
The bridge, which was completed in the 1930s, is beloved in Takoma Park, a suburban city of about 17,000 residents who live minutes outside of the nation's capital. The structure's three stately arches span a small stream, a parkway, and parkland, linking two key areas in the heart of the city.
The project has been on the priority list maintained by the Maryland State Highway Administration (SHA) ever since inspectors found extensive deterioration in the decking and later in the floor beams that landed the bridge on the structurally deficient list, according to Maurice Agostino, P.E., a project manager with SHA. The bridge is considered a prime candidate for rehabilitation rather than replacement because the robust reinforced-concrete foundations are in remarkably good shape, the span is eligible for listing in the National Register of Historic Places, and the community prizes its aesthetic charm. Rehabilitation also minimizes the impact on the stream and parkland below.
"Initially we were considering just doing the deck and replacing select floor beams. But once we got into it and really started looking at it, we [realized that] the best thing here is to rehabilitate everything above the arches," Agostino says. He notes that the SHA recently rehabilitated one of the other two such spans in the state and applied the lessons learned to this project.
"The abutments and the piers were in good condition," Agostino says. "Typically, any solid shafts or cantilever abutments that are big masses of concrete stand the test of time. There is very little work that needs to be done to them, besides a few minor spall repairs. The arches, overall, are in decent condition. We decided to replace all of the columns, floor beams, the deck, and parapets."
Workers are repairing damaged concrete on the arches and will soon begin removing the columns, beams, and decking above them, replacing them with cast-in-place members. © Maryland SHA
SHA hired Johnson, Mirmiran & Thompson (JMT), headquartered in Sparks, Maryland, as the prime engineering consultant on the project. The firm assessed the condition of the bridge's elements and developed computer models of the span that informed the demolition sequencing for the project. Kiewit Infrastructure, headquartered in Omaha, is the contractor.
The team will operate from an extensive demolition shield and platform to remove the structure above the arches, working from the center toward the approaches in a sequence developed to ensure the safety and stability of the arches. The arches themselves have already received extensive attention. Workers have meticulously sounded them with a hammer, finding areas where the concrete needs to be repaired.
"Tapping is a time-tested way to test concrete," Agostino says. "It is …effective in finding the bad areas." In those areas, the concrete is removed to a specified depth and reinforcement is added to ensure a strong repair. To date, most of the historic reinforcing members that have been exposed in the process are in good condition.
The new structural elements of the bridge will be cast-in-place concrete, made from molds that attempt to mimic certain aesthetics from the original design. "We could precast a lot of these elements, but what we found is that we would end up with lots of joints. And if the goal here is to extend the life of the structure for another 80 years, that would introduce opportunities for future corrosion," Agostino says. "We decided cast-in-place was the way to go to get the most durable structure."
The new deck will be wider by about 1 ft, enabling the SHA to include wider sidewalks that comply with the Americans with Disabilities Act (ADA) and add extra space for bicyclists. Because the bridge is considered a low-speed route, the design incorporates an open concrete balustrade—known as Texas Rail—that mimics the original parapet but provides greater safety in a crash.
The new, cast-in-place concrete elements will be married to the existing structure via dowels that extend out of the arches and into the spandrel columns. The project will use both the existing 1930s dowels, which will be exposed during the demolition process, and new dowels as needed. Once the bridge is complete, new and old sections alike will be power washed and stained a uniform tone to mimic a historic patina.
The most significant challenges of the project are logistical, Agostino explains. The bridge carries an average of 8,000 vehicles a day, providing a critical connection for emergency responders. The team had to develop a highly effective detour route and install new traffic signals to ensure it functioned as planned. The work site is also constrained to minimize disturbances to parklands and mature trees below. And the construction team had to create access areas along steep hillsides to facilitate ingress and egress during construction.
"This project is in the heart of a neighborhood. It is a heavily congested area," says Agostino. "Community involvement in this project was really key. We worked closely with the city—[which] owns the majority of roads around the site—to put together a detour plan and sell that detour plan to the community." The project includes a temporary pedestrian bridge for residents.
The SHA has placed a high premium on a short schedule for the rehabilitation. The contractor will have 12 months from the demolition in which to finish the structure, with incentives awarded for days not used and penalties incurred for any extra days needed.
"The goal is to have traffic back on the bridge about this time next year," Agostino says. "It's an 80-year-old structure that has stood up well, through the test of time. It will give us, hopefully, another 80 years."