William J. Donovan (Wilson Street) Bridge
- May 4, 2011
The existing Wilson Street Bridge, a three-span, earth-filled spandrel concrete arch structure built in 1911, needed to be replaced. City officials insisted that a new structure had to provide the aesthetic appeal of the existing design and to fit with the historic downtown neighborhood. To achieve this goal and others, the replacement bridge was designed as a three-span continuous cast-in-place concrete structure with parabolically shaped haunches and post-tensioned concrete deck slabs.
Use of High-Performance Concrete
The post-tensioned slab required a concrete compressive strength of 6,000 psi. The slab was prestressed in the longitudinal direction only, using 34 tendons with 19 0.6-inch-diameter strands in each tendon. High-performance concrete, including ground-granulated blast-furnace slag and silica fume, was used to increase workability during placement and increase the durability of the superstructure.
Epoxy-coated Steel Reinforcement
Epoxy-coated reinforcing steel was used throughout the deck slabs and in the cast-in-place pier, to protect against corrosion. The top of the piers were post-tensioned longitudinally with two tendons each consisting of 27 0.6-inch-diameter strands, while the pier’s base was post-tensioned longitudinally with four tendons each with the same number of strands. Post-tensioning the pier facilitated the arch shape while minimizing deflections and eliminating tension cracks through precompression.
Numerous aesthetic enhancements were incorporated into elements of the project, including architectural lighting, railings, sidewalk treatments, planters, precast concrete benches with pedestals for public art, river-observation patios and outlooks and reveal-patterned piers and abutments.
Three key factors provided by the concrete design ensured the project’s success: the post-tensioned concrete superstructure provided a thin structure depth; the structural concrete provided sculptural elements within the bridge’s structure; and the material’s flexibility created the flowing design required. These key factors allowed the structural engineers to deliver the client’s key expectations.