PROJECT BRATTLEBORO BRIDGE— A GATEWAY TO NATURE IN CONCRETE by Garrett Hoffman, FIGG

Construction of the Interstate 91 including its piers, viewing platforms, (I-91) Brattleboro Bridge Project in and railings, complements ’s Brattleboro, Vt., replaced twin existing natural landscape. The piers feature bridges over the with a new Vermont-inspired stone-formed long-span landmark bridge. The best and stained concrete that blends value-selected, design-build project was with the local environment. A visual designed by the team for the Vermont quality advisory team consisting of Agency of Transportation (VTrans). representatives from VTrans, the local The new gateway bridge features a aesthetic committee, and the bridge 1036-ft-long arching concrete bridge designer selected eco-friendly concrete soaring 90 ft above the West River stain colors, platform railing designs, and built using balanced-cantilever and other aesthetic details. construction. Two piers flank the river banks to support the three-span (263- The focal points of the bridge are the 515-258 ft) bridge. quad-wall piers, which emerge from the ground in sweeping organic forms Vermont’s Bridge to Nature and support the arching concrete spans. It was important to VTrans and the Each quad-wall pier is comprised of surrounding communities that the new four concrete columns that individually bridge serve as an icon and a gateway curve outward in two directions, creating to Vermont. The bridge construction a symmetrical pattern. The three- also needed to have minimal impact on dimensional (3-D) design and detailing the traveling public using the bridge, as of the columns resulted in a varying cross well as those traveling under the bridge: section and complex reinforcing steel vehicles on Vermont Route 30 (VT 30) (a configurations. The existing causeway along with the temporary major route for ski resorts), kayakers on trestles served as a working platform during the beautiful West River, and hikers on The designer, contractor, reinforcing construction. Note the difference in the new and the West River Trail. steel fabricator, and formwork provider old roadway elevations. held workshops to ensure that all details The design-build team was excited were considered and to provide the most about the challenge of designing and efficient design. The quad-wall system of constructing a beautiful, signature the piers provides stability, and allowed Every detail of the uniquely shaped structure that represents Vermont. the bridge superstructure to be built superstructure complements the natural Overlooking the West River and from above using balanced-cantilever Vermont landscape. Each quad-wall pier mountainous valley, this bridge features segmental construction without is comprised of four concrete columns viewing platforms for pedestrians, temporary falsework in the river. This that curve outward in two directions, hikers, and visitors. True to its theme, scheme minimized the impact of the symbolizing stone trees emerging from “A Bridge to Nature,” every detail of project on the West River and West River the ground and supporting the arching the uniquely shaped superstructure, Trail. concrete spans. All Photos: FIGG.

INTERSTATE 91 BRATTLEBORO BRIDGE / BRATTLEBORO, VERMONT profile BRIDGE DESIGN ENGINEER: FIGG Bridge Engineers Inc., Exton, Pa. ROADWAY/GENERAL CIVIL ENGINEER: Sebago Technics Inc., South Portland, Maine PRIME CONTRACTOR: PCL Civil Constructors Inc., Raleigh, N.C. POST-TENSIONING CONTRACTOR: DSI, Freedom, Pa.

22 | ASPIRE Winter 2018 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 The new gateway bridge in Brattleboro, Vt., carries Interstate 91 over the West River, texture below. 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. Community Involvement Using self-advancing formwork (form aesthetic as the bridge spans the The design-build team led monthly travelers), 16-ft-long segments of the valley. With a depth of 12 ft 7 in. at “trail talks” to give the community the bridge were cast-in-place, alternating midspan and 30 ft 7 in. at the piers, opportunity to walk up the West River from one side of the pier to the other, the segments were large relative to the until each cantilever arm reached human scale. The biggest segments 252 ft. When the cantilever arms on contain 221 yd3 of concrete and took adjacent piers were complete, a small 6 hours to cast. Another unique feature closure segment was cast to connect of the box-girder section is the vaulted- the two cantilever arms and form the bottom soffit that runs the full length span. Surveying and geometry control of the underside of the bridge. This were a full-time endeavor to ensure that 20-ft-wide, 4-ft-deep, barrel-like shape the two cantilevers would meet at a adds dimension to the soffit, which precise, midair target. Prior to casting would otherwise have a flat 55-ft-wide the closure segment, the two cantilevers surface. were longitudinally jacked apart to mitigate long-term creep and shrinkage Continuous mild reinforcement through effects on the relatively stiff quad-wall segment joints and a grouted post- pier system. tensioning system create continuity of the cast-in-place segments. Top slab Segmental Superstructure tendons were used during cantilever To support the 104-ft-wide bridge construction, while bottom slab and deck carrying two lanes of traffic in external draped tendons provided each direction, a two-cell, three-web continuity after span closures were cast. trapezoidal box girder was used. The Transverse top slab tendons balanced use of a single bridge instead of twin the deck design. All tendons have Cantilevers of piers 1 and 2 poised to bridges eliminated a major traffic shift multiple layers of corrosion protection, meet to complete the 515-ft main span and crossover section and improved including a 2¼-in.-thick integral over the West River. Two-way traffic was mobility during construction. A variable- wearing surface, increased concrete maintained on the existing southbound depth profile was used for structural cover, low-permeability concrete, plastic Interstate 91 bridge until the new bridge efficiency and provided a natural ducts, and grout. was finished and ready for traffic in March 2017.

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.

ASPIRE Winter 2018 | 23 Trail to the bridge with the team and Durability learn about the design and construction VTrans required a 100-year design of the monumental bridge. life, but the bridge designers focused The bridge designer also created on providing a 150-year design life. 3-D-printed models of the bridge in Concrete segmental bridges as a snap-together pieces to make hands- structure type are inherently durable on learning tools for student education due to sustainable materials and the programs at Brattleboro-area schools. use of biaxially post-tensioned concrete. During both design and construction, Concrete mixture proportions were the design-build team visited several designed for low permeability and the local schools to discuss the construction addition of calcium nitrite enhanced and engineering behind bridge building. resistance to chloride penetration. Also, Custom FIGG Bridge Boxes, which stainless-steel reinforcing bars were Pedestrians enjoy the West River Trail contain education tools to inspire used in the bridge deck to enhance the and provide scale to the grand 60-ft-tall and teach children about science and deck life. Incorporation of durability into quad-wall piers of the bridge. The piers engineering, were part of the project the initial design will ensure the least have a textured concrete surface inspired activities. possible maintenance and cost over the by the area’s native stone. The barrel life of the bridge. shape cast into the soffit is colored blue On Saturday, March 4, 2017, more than to match the sky. 800 local residents and visitors took Conclusion advantage of an opportunity to walk The design-build team provided creative footings and abutments, it required across the new bridge before it opened solutions to the bridge challenges, less erosion control and had fewer to traffic. Representatives from VTrans including the use of balanced-cantilever areas of environmental impact during and the design-build team were on construction, which eliminated the construction than the original bridge hand to answer questions as the public need for temporary falsework in concept during the request-for-proposal journeyed across the bridge. The bridge the West River. Compared with its phase. The single concrete bridge also was dedicated on September 12, 2017. predecessor, the single bridge provides provides ease of inspection inside the a smaller overall footprint. With fewer bridge, requiring less mobilization during future annual inspections. A best-value concrete segmental solution provided a one-of-a-kind gateway to nature in the beautiful state of Vermont.

______

Garrett Hoffman is the northeast regional director for FIGG in Exton, Pa.

Balanced-cantilever construction allowed work to continue through the harsh Vermont winters. No temporary falsework was needed, which kept crews out of the water and allowed Construction of Pier Table 1. Pier 1 soared 70 ft in the air while vehicular traffic was construction to continue on both sides of maintained on Route 30 and river remained open for recreational boating. the river.

24 | ASPIRE Winter 2018