Each tower has lower legs that lean outward on a radius and taper in both dimensions, a hollow lower cross strut at the roadway level, and hollow upper legs on a radius leaning inward and tapering in one dimension.
Building the towers depended heavily upon a flexible formwork system that consisted of several sets of formwork. The lower legs, lower strut, upper legs, the stay anchors, and the upper strut-each section each required a separate set of formwork and a completely separate set of work platforms.
A trestle built out from each shoreline provides access to the pylon foundations. Almost all of the concrete for the lower legs was pumped, with the pump trucks located on the trestle ends that had been expanded and reinforced specifically for this purpose. Concrete for the upper legs was placed with crane and bucket.
The lower legs required four 15-foot mass concrete pours. Because that concrete required an extended cure time, the forms for each leg were designed to allow the contractor to use a leapfrog process.
The contractor is using two large tower cranes (one at each tower) adjacent to the pylon foundations in the river channel. The foundations themselves began as precast footing boxes, each roughly 100 feet long, 50 feet wide, and 16 feet tall.
The East End Crossing bridge features two convex diamond-shaped reinforced concrete towers or pylons that rise 300 feet above the water to support a 1,200-foot main span.
Because the upper towers are hollow, thermal control was not nearly as much of a requirement, allowing the contractor to cycle the formwork faster. That required a concrete that could achieve strength faster to accommodate the formwork cycle, a significantly different concrete mix than was used in the lower towers.
Building the lower strut and the knuckles, where the lower strut connects and the legs change direction, posed significant challenges. Constructing the cross strut and knuckles took the better part of four months.
As the tower height increased, a compression strut made from a shoring tower was built into the formwork to limit deflection of the inward leaning concrete legs. Formwork sections for the upper horizontal strut were preassembled and flown in, just as they had been for the lower strut.