The New IH35W Bridge – Minneapolis, Minnesota

The new I-35W Bridge, an emergency replacement for the steel girder bridge that collapsed on August 1, 2007, consists of twin bridges 1,223’ long with a 504’ precast segmental main span across the Mississippi River in Minneapolis, Minnesota. This segmental concrete “smart bridge” features a progressive design of new technology and achieves the owner’s vision for quality, safety and innovation. Close coordination of the design/build team allowed for the successful completion of the new I-35W Bridge within the accelerated schedule and set a new standard for speed and innovation in design/build projects. Designed to carry 10 lanes of interstate traffic, the new I-35W Bridge is also transit and suspended pedestrian bridge ready to meet Minneapolis’s changing transportation needs.

Innovation of Design and/or Construction

Innovative concrete set the stage for a segmental bridge design with an over 100-year life. High-strength, high-performance concrete was used to cast the new bridge structure. Most concrete was placed during a harsh Minnesota winter, with -40 degree wind chills, requiring special mix designs to maintain proper temperatures.

Over the service life of the bridge, information collected from 323 sensors embedded in the concrete throughout the bridge will assist in managing operations by enhancing bridge inspections with structure performance data; maintaining efficient and safe traffic flow; and providing infrastructure security. The sensors measure the bridge’s response to loads in real-time to alert officials when there is the potential for a problem before it occurs. When temperature, humidity and wind speeds reach specified levels, the sensors on the main span trigger the bridge’s automated anti-icing system. The information gathered from the sensors will provide valuable feedback about bridge traffic patterns, infrastructure maintenance and design sustainability for future bridges.

Low energy, low maintenance Light Emitting Diode (LED) lights were used throughout the project. The nighttime signature for the bridge is achieved through LED lights, allowing for reduced costs, maintenance and an array of color choices. LED highway lighting, its first use in the United States, was also implemented on the new bridge. The energy savings and effects of this new lighting method are being studied in conjunction with the Department of Energy to explore ways to reduce energy consumption in outdoor lighting applications across America.

In the future, lane configurations may be adjusted to add vehicular, HOV, bus or light rail lanes. Provisions for a future pedestrian bridge were also included in the plans for the new interstate bridge.

Rapid Construction

The new I-35W Bridge was opened to traffic on September 18, 2008 – more than three months early. The entire emergency replacement structure was designed and built in 11 months to restore a vital transportation link in the heart of downtown Minneapolis.

One of the biggest time savers was combining construction methods. It is unusual to use both cast-in-place and precast construction on the same job, but doing so allowed for spans over land on both sides of the river to be constructed on temporary steel falsework while the box girder segments for the main span over the river were precast in the casting yard. Eight casting beds were built to allow for casting of all 120 segments in as little time as possible. Proceeding out from both sides of the river toward the center, cantilever construction of the 504’ main span over the Mississippi River began on May 25, 2008 and was completed just 47 days later. From notice-to-proceed to completion of the main span of this 10 lane interstate bridge over the Mississippi River was only 9 months.

Aesthetics and/or Harmony with the Environment

The theme of “Arches-Water-Reflection” inspired the lines, proportions and aesthetic features of the new I-35W Bridge. The modern curves are a salute to the historic arch bridges along the corridor. Water, the centerpiece of the project, is framed to pay homage to the power and importance of the great Mississippi River. Reflection refers to both literal reflection, as is often captured in the river, and the spiritual reflection of the site.

At night, lighting accentuates the reflective curves of the 70’ tall piers as they rise to meet the sweeping parabolic arch of the superstructure. Rip rap and native landscaping surround trails below the bridge and are juxtaposed with accents of stainless steel to blend the modern, white bridge with its river environment. These trails tie into existing trails around the city and lead to plazas at the waters’ edge that offer unique views of the river. Conceived as a functional sculpture within the existing landscape, the bridge celebrates and preserves its site while incorporating great redundant strength and new technology.

Cost Competitiveness

The contract for the new I-35W Bridge was designed as a “Best Value” design/build project, combining both the final bid price, technical merit, and schedule into the final score. The owner’s experience with design/build projects allowed them to facilitate award of this contract quickly. Through creative planning, the design/build team was able to accomplish the bridge under budget for a cost of $234 Million, while also completing the innovative bridge ahead of schedule and with a remarkable safety record.

Minimization of Construction Impact on the Traveling Public

At a cost to the local economy of nearly $400,000 per day, quick restoration of the I-35W crossing was crucial to minimize impacts on the community. The design/build team worked quickly to restore the crossing, finishing more than three months early, allowing the community to return to normal routines.

Because of the circumstances leading to the construction of the new I-35W Bridge, working with the community to help restore confidence in the structure was also important. The design/build team and owner worked together throughout the project to keep the community informed about progress, answer questions about construction and the new bridge, and to gain their acceptance of the new structure.

Jury Comments

This project incorporates innovations in design and construction in meeting the desires of the community, enhancing the environment, assuring sustainability, quality, and economy. The high level of cooperation between the owner, builder and contractor resulted in this significant construction achievement. This project exceeded expectations under very demanding requirements.