Epoxy Interest Groupxx

The new Highway 43 Bridge 85851 over the Mississippi River in Winona, Minnesota, which opened to traffic in August 2016, carries one lane of traffic in each direction and includes a 12-foot-wide sidewalk. This new 2,300-foot-long segmental box girder structure complements the adjacent 1942 bridge and features a 450-foot long main-span with sleek pier shapes and aesthetic elements that were developed through Community input and voting.

The existing Bridge 5900, featuring a three-span steel-riveted cantilever through-truss, is being rehabilitated and its approach spans are being reconstructed. When completed in 2019, this renovated structure will carry two lanes of northbound traffic with the new Bridge 85851 carrying two lanes of southbound traffic.

For the first time, officials at the Minnesota Department of Transportation (MnDOT) commissioned the project under the Construction Manager/General Contractor (CMGC) method of procurement. The goal was to speed up the project by initially breaking it into two work packages.

“As the process evolved, MnDOT realized the need to break out these work packages further to help accelerate construction and meet critical deadlines,” explains John Dvorak, senior bridge engineer with FIGG. “Ultimately, six work packages were necessary to complete the project and MnDOT’s forward thinking, along with a dedicated contractor, resulted in early completion of the new bridge for an already aggressive schedule.”

The new bridge consists of a four-span unit with a cast-in-place, post-tensioned concrete slab and a five-span unit of 63-inch-deep precast, pretensioned concrete girders. It transitions to a three-span, single-cell, segmental box-girder unit built using the balanced cantilever method with form travelers, followed by the final four span unit of 63-inch-deep precast, pretensioned concrete beams on the north approach.

The concrete box-girder structure type was selected in part for its visual impact, which was planned to complement the adjacent historic bridge, according to Terry Ward and Keith Molnau at the Minnesota Department of Transportation. The girder design also helped keep the river crossing open during construction using overhead form travelers for construction.

The three-span unit features 242-foot end spans flanking the 450-foot main-span, which aligns the piers with the historic bridge. The girder’s bottom slab tapers from 4’-9” thick at the face of the pier diaphragms to a minimum of 9 inches thick 140 ft from the centerline of the pier. The girder’s haunches mirror the shape of the historic bridge and were found to be the most cost-effective approach. The balanced-cantilever method of construction limited falsework to the pier tables that stayed within the USCG navigational construction envelope limits.

Several provisions were included by MnDOT to provide a 100-year design life. For the segmental box girder, durability is increased with a 50-psi residual compression requirement in the top of the deck under normal service loading, a two-inch thick integral wearing surface, and stainless-steel reinforcing bars in the top slab.

MnDOT’s standard policy includes epoxy-coated reinforcing in its substructures and superstructures. Epoxy-coated reinforcing was used in the main-span segmental superstructure, although stainless-steel reinforcing was substituted in the deck, an approach MnDOT considers more effective on a life-cycle basis. Epoxy-coated reinforcing was also used in the flat slab at Unit 1, and in the deck and precast beams at Units 2 and 4.

Additional durability requirements included the use of high-performance concrete with contractor-provided mixture proportions, achieving a compressive strength of 7 ksi in the flat slab and segmental units. Ranges on cement, fly ash, and slag were required, along with low-absorption aggregates and limitations on shrinkage and scaling.

A deck-level sidewalk, lit by LED accents, provides pedestrian access, with overlooks positioned along the spans.