John Street Bridge replacement earns engineering honors

The John Street Bridge Replacement project has been honored with the 2014 Structural ACE Award of Merit from the Connecticut Society of Civil Engineers.

Led by the Department of Public Works Engineering Division, the project showcased innovative design and impressive implentation. The award was delivered as a part of the seventh annual Achivement in Civil Engineering (ACE) Awards Ceremony.

Spanning the Byram River, the original John Street Bridge was built in 1921 and after some 90 years of use, the bridge was in need of replacement. Project planners set out to create a replacement that would address the narrow width of the original bridge, while minimizing the impact the construction would have on local traffic.The John Street Bridge is a primary route for school buses, serving as an artery between Round Hill Road and Riversville Road.

Strucutural weaknesses in the bridge were corrected through the installation of a precast concrete rigid frame structure. The structure has a minimum 50-year expected service life. Additionally, the new bridge has a width of 28-feet, up from the original’s 19’ 10” width, allowing for two 12-foot travel lanes and a pair of 2-foot shoulder. Guard rails and rinforced concrete parapets were added to the bridge to increase safety measures as well.

The Town’s goals for the John Street Bridge replacement were satisfied and completed under budget, making the project an absolute success. Other winning civil engineers included construction design engineersd Fuss & O’Neill , construction management group AI Engineers and contractor A. Vitti Excavators, LLC.

The original bridge was built in 1921 over the Byram River in the northern portion of Greenwich. The bridge consisted of a 15-foot span concrete slab on concrete abutments with a curb to curb width of 19’-10”, compared to approach roadway widths of approximately 28 to 30 feet. The hydraulic opening under the bridge was inadequate, with flood water overtopping the road during a 25-year storm event and overtopping by 2.42 feet in a 100-year storm event.

The design team addressed these challenges in a number of ways. First, the structural deficiency was corrected by replacing the bridge with precast concrete rigid frame structure with a minimum 50-year expected service life. The new bridge’s 28-foot total width provides two 12-foot travel lanes and two 2-foot shoulders, matching the approach roadway widths.

The new roadway is super-elevated at 6% across the bridge to maintain a 25 mile-per-hour design speed. Safety was further enhanced with reinforced concrete parapets and approach guide rail systems. In order to increase the waterway opening and reduce the severity of the sag vertical curve, the roadway profile was raised 2.44 feet. Combined with a longer 25-foot span and reduced 18 inch superstructure depth, the low chord of the bridge now passes the 100-year flood flow with one foot of freeboard. Approximately 550 feet of John Street was reconstructed to transition the new roadway profile and alignment into the existing roadway.

The roadway alignment and bridge wing wall configurations were designed to minimize impacts to adjacent properties and environmentally sensitive areas.

The management and execution of the planning, design and construction observation phases were performed effectively and efficiently thereby allowing the town of Greenwich’s goals to be met. This project was set as a priority by the Town. We are very proud of the John Street Bridge and exceptionally honored to be recognized by the Connecticut Society of Civil Engineers.

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