Rebuilding a bridge before the holidays
New Jersey Department of Transportation / Livingston and East Hanover Townships, New Jersey
After more than 80 years of service, the deck of the Route 10 Bridge over the Passaic River was in poor condition, with exposed and rusted reinforcement, and several large spalls and areas of scaling with efflorescence on the underside of the deck. The bridge was considered functionally obsolete due to its narrow width and structurally deficient due to the condition of the deck.
Because Route 10 is a busy commercial corridor with average daily traffic of over 44,000 vehicles with peak traffic periods on Saturdays, rehabilitating the bridge presented several challenges. Route 10 provides access to a popular commercial corridor, including box retail stores, strip malls, small stores, and office space with numerous driveways.
To limit disruptions to the various stakeholders, it was critical that the project be advertised, awarded, and constructed in less than one construction season. Traffic impacts had to be minimized during the school year, and work had to be completed well before the holiday shopping season.
In 2009, the New Jersey Department of Transportation retained Mott MacDonald to provide study phase services for the replacement of the bridge deck. At the beginning of the study phase, we prepared a Bridge Design Appraisal Statement to assess in more detail the initially scoped deck replacement project. Based on the relatively short 34-foot spans, the concrete encasement of the existing 30-inch steel beams, and the embedment of the top flanges in the deck, we determined that it would be too time-consuming to remove the deck without damaging the beams.
Mott MacDonald therefore recommended replacing the full superstructure and suggested the use of prefabricated bridge units, which would greatly reduce the construction duration compared to installing individual bridge beams and subsequent cast in place concrete deck construction. Initially, prefabricated steel beam bridge units with a composite concrete deck were considered.
However, at the beginning of the preliminary design phase and together with NJDOT’s bridge design subject matter expert, it was decided to use precast prestressed concrete double-T section bridge units, known as NEXT Beams®. Unlike their steel beam counterparts, the prefabricated concrete beam units would not require one or two maintenance paintings during their service life. Each section would have a full-thickness top deck flange, eliminating deck formwork and cast-in-place reinforced concrete deck construction. The NEXT Beam® units are connected with narrow closure pours using high-performance concrete and the system was topped with a high early strength concrete overlay to provide a smooth riding surface.
As part of the design process, Mott MacDonald performed stability checks of the existing concrete abutments during the staged demolition and construction and it was determined that the abutments may be unstable after superstructure demolition and before the replacement superstructure was in place. To improve the stability of the existing abutments, 60-foot-long inclined ground anchors were designed to be cored through and installed in the abutment stems just below the bridge seats back into the approach roadway embankments. The anchors would be grouted in place, allowed to cure, and tested for confirmation of their required load capacity.
To allow for the ground anchor installation before the superstructure demolition, holes were saw-cut in the deck between the existing stringers. After the ground anchor installation, the existing bridge superstructure was then saw-cut longitudinally between the bridge beams and lifted out in sections, together with the attached deck sections. The two outermost stringers supporting the bridge parapet and sidewalk were removed in one piece. The bridge and pier seats were then reconstructed and the new NEXT Beam® bridge units installed.
Prefabricated, precast concrete approach slabs were used immediately behind the abutments to transition from the bridge to the approach roadways, and were connected with closure pours and topped with concrete overlays similar to those used on the bridge.
Due to a lack of space adjacent to the highway’s right-of-way, as well as adjacent development and environmentally sensitive parcels, a temporary bridge and diversionary roadway were not feasible. Mott MacDonald developed construction staging and traffic control plans to maintain westbound Route 10 traffic on the bridge. Eastbound traffic was detoured onto an adjacent county roadway, Old Mount Pleasant Avenue.
Despite challenging site conditions, the project met the owner’s goal of rehabilitating a bridge serving a busy highway within a single construction season and well before the holiday traffic season.
The use of accelerated bridge construction techniques reduced the construction duration by 50% compared to standard cast-in-place construction of the concrete components. More significant reductions in construction time would have been possible if the abutments had not required stabilization.
The widening of the bridge will provide added safety for motorists and will remove the bridge from the functionally obsolete category. The new superstructure and substructure repairs will also remove the bridge from the structurally deficient category.
Construction techniques were designed in order to protect environmentally sensitive wetland parcels downstream from the bridge along both banks of the Passaic River.