The New Dresbach Bridge – La Crescent, Minnesota / La Crosse, Wisconsin

The new I-90 Dresbach Bridge demonstrates how a concrete segmental solution creates a beautiful, efficient, long-span bridge while being built in sensitive environmental conditions, through harsh winter weather, at the same time achieving a new record span length for Minnesota. Its concrete segmental superstructures, with custom pier shapes, achieve context sensitive, signature designs while being economical and delivered ahead-of schedule. This innovative concrete segmental bridge solution met or exceeded all of Minnesota DOT’s project vision, criteria, and goals for this new Mississippi River crossing.

The New Dresbach Bridge has wide shoulders providing ample space and is designed to exceed current structural and geometric standards. The new, modern, and ecologically conscious four-lane bridge features twin concrete segmental variable-depth box superstructures that vary in width between approximately 66’ and 45’. Over the main channel of the Mississippi River, the new four-span bridge consists of twin, post tensioned concrete segmental structures with record-setting dual 508’ main spans (longest concrete span in Minnesota), built from above with form travelers in balanced cantilever. Construction was kept to the smallest footprint to protect the environment, adjacent recreational facilities, and USCOE Lock and Dam No. 7 just upstream. The dual 508-foot-long main spans resulted in only one pier near the main channel of the river and provide a commercial navigation opening larger than the minimum required by the U.S. Coast Guard.

Innovation of Design and/or Construction

Design criteria was developed that met MnDOT’s goal of exceeding the robust durability benefits of post-tensioned concrete segmental design and went beyond the typical criteria required by AASHTO. This resulted in implementation of the following innovative items:

The use of stainless steel reinforcing in the bridge decks. MnDOT continues to lead the industry in the development of specifications and details for the use of stainless steel reinforcing in all types of bridges.
Polypropylene duct for post-tensioning tendons. Galvanized and epoxy coated anchors specified based on location to maximize durability.
The use of post-tensioning tendon grout meeting the latest PTI specifications including current interims that do not permit the use of inert filler.
Research, specifications, and in-place performance testing of innovative thin premixed polymer concrete deck overlay at discrete locations such as where temporary access holes were used during construction.
Lower tensile stress limits than required by AASHTO.
Requirement for long-term bi-directional compression across temporary construction access hatches in the deck.
Finite element moment curvature analysis to determine refined substructure stiffness in lieu of AASHTO approximate methods.
Site-specific thermal analysis representative of the local conditions in Minnesota.
Force-pulse (statnamic) dynamic load testing of large diameter steel pipe piles to more accurately determine pile capacity and allow higher resistance factors reducing the number of piles required.
100-year service life for enhanced durability and low maintenance.

In addition, the New Dresbach Bridge is designed to accommodate a future pedestrian bridge suspended beneath and between the eastbound and westbound structures. A unique catenary-suspension bridge design was developed to the level needed to ensure that the bridge can accommodate resulting loads. Anchorages were fully designed and included in the new bridge. This is easy to accomplish using concrete segmental bridge design.

After cancellation of a WisDOT light rail project, it had a pre-purchased stockpile of H-piling. The New Dresbach Bridge east-channel foundations were designed for this specific piling, and the stockpile was transferred from WisDOT to MnDOT. Both agencies benefited: MnDOT through significant cost savings to the project and WisDOT by removal of the piling from its inventory.

Rapid Construction

The concrete segmental bridge design allowed means and methods that provided simple solutions to the complex site. To accelerate construction, this bridge was built in four directions at once, in balanced cantilever, from two piers at a time using two sets of form travelers. ASBI and PTI certified crews with experienced construction leadership cast an average of four segments per week for the eastbound bridge, while the westbound bridge frequently produced six segments per week, without the need for a second or third shift. One hundred-foot-long sheet piling was used for the nearly 80-foot-tall cofferdams needed to install the main-span unit foundations. Due to the cofferdams, the contractor could construct all the piers but one within the first two construction seasons, keeping the project on-schedule despite heavy spring flooding and a difficult winter. Once the superstructure was complete, only the barrier operation remained before the structure was opened to traffic, saving schedule over non-segmental bridge types and allowing the river bridges to be off the project CPM critical path. At the peak of construction, 270 people worked on the project ensuring that the rapid construction delivered the project to Minnesota DOT ahead of schedule. The twin wall pier shapes provided the function of extra stability during cantilever construction without needing temporary supports in the Mississippi River. This enhanced speed of construction, cost efficiency and safety.

Saving long-term agency costs on maintenance, the bridge provides a highly-redundant river crossing with an enhanced lifespan of more than 100 years. Furthermore, the use of concrete spurred the local economy by using local labor and materials, increased local employment and wages, and allowed tax dollars to be invested back into local businesses and communities for continued economic growth.

This project exemplifies the cost-advantages of concrete segmental bridge structures. MnDOT awarded the project for a low bid of $81.5M (bridge only). With a per square foot cost of $305, the new Dresbach Bridge provided a cost savings to MnDOT compared to other similar state projects while achieving a record concrete span for Minnesota. The New Dresbach Bridge is the perfect example of how concrete segmental bridges provide a durable, low-maintenance, and sustainable solution for the lowest life cycle costs, which is a goal for funding-challenged transportation systems.

Aesthetics and/or Harmony with the Environment

Located within the Upper Mississippi River National Wildlife and Fish Refuge, the New Dresbach Bridge serves as a model for how a grand bridge can be developed to exist harmoniously with, and honor, the landscape and environment. The design inspiration for the new river bridge came from the natural, picturesque landscape of the surrounding area. The portion of the bridge crossing the main channel of the Mississippi River requires functionality and contextual aesthetics both within the environment and at a pedestrian level. The aesthetic details of this bridge were selected by members of the community through a series of meetings, including pier shape, railing details, bridge color, and abutment and retaining wall treatments.

Minimization of Construction Impact on the Traveling Public

The twin wall piers created engineering balance during the superstructure construction without any temporary supports in the river, keeping maritime traffic moving. Since it was built from above, there was no need for large ground- and water-based equipment, allowing unrestricted river traffic during construction which met a critical need for the USACE Lock and Dam No. 7 located just upstream.

Jury Comments

This bridge’s structural elements provide aesthetically pleasing shapes and forms with the capacity to deliver a record setting concrete span over a major waterway for its owner. It is a world class Mississippi River crossing bridge, inclusive of innovative approaches to design, materials, and rapid construction. The twin wall piers were nicely integrated in harmony with the Mississippi River crossing.