Cantilever Construction for Unhindered Traffic
Within the scope of a construction project in Brattleboro, Vermont, in northeastern USA, four old bridge structures are being replaced by two new bridges. The larger of the two, bridge 9, will accommodate the Interstate 91 motorway on 4 lanes, thus eliminating the current road traffic bottleneck in this area.
A total of 535m³ (700yrd³) of concrete had to be poured for the bridge foundation – more than any other project in Vermont. The new structure is approx. 316m (1,036ft) long and has a 157m (515ft) long main span as well as two approx. 80m (263ft) and 79m (258ft) long side spans. The segmental bridge is being constructed using the free cantilever method to minimize construction time and to avoid any negative impact on the local natural environment.
The 31.7m (104ft) wide main span is located approx. 30.5m (100ft) above the water surface and includes viewing platforms at each of the curved bridge piers permitting a view of the beautiful countryside.
Types 4-0.6", 12-0.6", 19-0.6" and 27-0.6" DYWIDAG Strand Tendons were predominantly used as post-tensioning systems in the bridge. Approx. 539t (594 US ton) of Grade 270 strand were needed for the tendons. 814 flat anchors were provided for the transverse tendons in the top slab of the box girder. The anchors were reinforced with stainless steel in the anchor zone due to a contract requirement.
The cantilever and continuity tendons consisted of 8 Type 12-0.6" DYWIDAG Tendons, 57 Type 19-0.6" DYWIDAG Tendons and 90 Type 27-0.6" DYWIDAG Tendons in corrugated polypropylene duct. Furthermore, 44 Type 27-0.6" DYWIDAG Tendons were used as traditional external tendons.
DSI USA also supplied 22.7t (25 US ton) of permanent 36mm Ø, Grade 150 DYWIDAG Bar Tendons that were installed longitudinally in the superstructure and at the tops of the piers. In addition, DSI provided detailed assembly drawings and engineering support and rented the equipment needed for stressing.