THE CONCRETE BRIDGE MAGAZINE

WINTER 2018

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/922349

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Using self-advancing formwork (form travelers), 16-ft-long segments of the bridge were cast-in-place, alternating from one side of the pier to the other, until each cantilever arm reached 252 ft. When the cantilever arms on adjacent piers were complete, a small closure segment was cast to connect the two cantilever arms and form the span. Surveying and geometry control were a full-time endeavor to ensure that the two cantilevers would meet at a precise, midair target. Prior to casting the closure segment, the two cantilevers were longitudinally jacked apart to mitigate long-term creep and shrinkage effects on the relatively stiff quad-wall pier system. Segmental Superstructure To support the 104-ft-wide bridge deck carrying two lanes of traffic in each direction, a two-cell, three-web trapezoidal box girder was used. The use of a single bridge instead of twin bridges eliminated a major traffic shift and crossover section and improved mobility during construction. A variable- depth profile was used for structural efficiency and provided a natural aesthetic as the bridge spans the valley. With a depth of 12 ft 7 in. at midspan and 30 ft 7 in. at the piers, the segments were large relative to the human scale. The biggest segments contain 221 yd 3 of concrete and took 6 hours to cast. Another unique feature of the box-girder section is the vaulted- bottom soffit that runs the full length of the underside of the bridge. This 20-ft-wide, 4-ft-deep, barrel-like shape adds dimension to the soffit, which would otherwise have a flat 55-ft-wide surface. Continuous mild reinforcement through segment joints and a grouted post- tensioning system create continuity of the cast-in-place segments. Top slab tendons were used during cantilever construction, while bottom slab and exter nal draped tendons provided continuity after span closures were cast. Transverse top slab tendons balanced the deck design. All tendons have multiple layers of corrosion protection, i n c l u d i n g a 2 ΒΌ - i n . - t h i c k i n t e g r a l wearing surface, increased concrete cover, low-permeability concrete, plastic ducts, and grout. User Experience Travelers along VT 30 experience this distinctive bridge from a side vantage point before they then travel under the bridge. They see the vaulted soffit stained with a blue color to mimic the sky. The arching, long span of the superstructure is half as deep as the former bridge and opens up the view of the landscape. To match the surrounding environment, a permanent concrete earth-toned stain was applied to all sides of the bridge superstructure. The piers were cast with a texture that simulates Vermont stone, which creates a dramatic look with different natural colors along the 60-ft-tall piers. The upper "fins" of the piers cradle the superstructure and were hand-sculpted using shotcrete to match the stone texture below. Community Involvement The design-build team led monthly "trail talks" to give the community the opportunity to walk up the West River VERMONT AGENCY OF TRANSPORTATION, OWNER BRIDGE DESCRIPTION: The new bridge is a 1036-ft-long three-span segmental cast-in-place concrete box girder bridge built utilizing balanced- cantilever methods with form travelers. STRUCTURAL COMPONENTS: A single dual-cell segmental concrete box girder with transverse and longitudinal post-tensioning with an overall deck width of 105 ft. The new gateway bridge in Brattleboro, Vt., carries Interstate 91 over the West River, Vermont Route 30, and the West River Trail. Located in southern Vermont, the bridge provides a visual "gateway" to the state's mountains, valleys, and rivers. Cantilevers of piers 1 and 2 poised to meet to complete the 515-ft main span over the West River. Two-way traffic was maintained on the existing southbound Interstate 91 bridge until the new bridge was finished and ready for traffic in March 2017. ASPIRE Winter 2018 | 23

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