ASPIRE is a quarterly magazine published by PCI in cooperation with the associations of the National Concrete Bridge Council. The editorial content focuses on the latest technology and key issues in the Concrete Bridge Industry.
Issue link: http://www.aspiremagazinebyengineers.com/i/335723
ACCELERATED BRIDGE CONSTRUCTION State Route 112 Bridge over Kearney Brook. By Michael P. Culmo, CME Associates Inc. The Massachusetts Department of Transportation (MassDOT) is nearing the completion of an Accelerated Bridge Program (ABP), which has a goal of reducing the number of deficient bridges on an accelerated schedule. The ABP has embraced innovation—especially including the use of accelerated bridge construction (ABC)—in order to deliver projects faster, with better quality, and with less impact to the traveling public and environment. The State Route 112 Bridge that spans over Kearney Brook, in Worthington, Mass., is an excellent example of this use of innovation. The existing bridge needed to be replaced due to significant deterioration. The original scope of the project was based on using adjacent box beams supported on conventional cast-inplace concrete abutments. Because the roadway crossing the brook is on a horizontal curve, the box beams would need to be chorded on the curve. The plan was to close the roadway during construction. The detour around the site was only 1 mile; however, the impact of the detour on the rural town would be significant because local roads would need to be used. During preliminary design, MassDOT made a decision to use ABC to reduce mobility impacts. At the same time, the department had adopted a new prestressed concrete beam shape called the Northeast Extreme Tee (NEXT) beam. It is a double-tee beam developed by the PCI Northeast Bridge Technical Committee for intermediate span bridges up to approximately 80 ft long. NEXT beams were a perfect choice for the 62-ft-long, single-span crossing. The design team selected a 32-in.-deep NEXT F (form) beam with a 4-in.-thick top flange used to support an 8-in.-thick composite, cast-in-place concrete deck. Once erected, the flange provides a safe work platform. The specified compressive strength of the concrete for the beams was 8.0 ksi. The forming of the deck is limited to the side and end forms. Design Challenges The geometry of the single-span bridge is curved and skewed at 30 degrees, which would put the flexibility of the NEXT beams to the test. The first challenge was the horizontal curvature. The radius of the roadway resulted in a variation of the deck edge of approximately 10 in. when measured from a chord line. The NEXT beams were developed to accommodate this type of curvature. The beams were laid out on tangents, and the curvature was accommodated by varying the width of the fascia beam overhang along the beam length. MassDOT commonly leaves existing substructures in place to act as scour countermeasures. To accomplish this, the span length was increased to allow for construction of the new abutments behind the existing abutments. This eliminated work in the river channel. The depth to the bedrock was too deep for open excavation and too shallow for an integral abutment, so the design team decided to use a shallow spread footing foundation. Precast Concrete Details The design team used precast concrete substructure details that were developed by the PCI Northeast Bridge Technical Committee, including precast concrete spread footings, abutment stems, wingwalls, and approach slabs. Precast concrete footings were placed on temporary leveling bolts and connected to the substrate with a thin layer of flowable fill. The wingwall stems were connected to the footings with (continued next page)