The 10th Avenue SE Bridge in Minneapolis is a critical transportation element that crosses over the Mississippi River and is near the University of Minnesota. Each day, the bridge carries ~10,000 motor vehicles as well as hundreds of bicyclists and pedestrians over the river. Built in 1929 and serving the City for more than 90 years, the bridge is listed on the National Register of Historic Places.
The 10th Avenue SE Bridge is 2,163 ft. in length, nearly 70 ft. wide and features 21 spans (7 main river spans and 14 approach spans). The bridge is one of the highest (115 ft. above the river) and longest concrete arch bridges in the Midwest.
Identifying the need for bridge rehabilitation
In recent years, leaking expansion joints and drainage elements have led to deterioration of critical concrete components. This deterioration was a mixture of freeze-thaw damage and corrosion from years of de-icing chemical use.
The City sought a multidisciplined partner to design and lead a thorough rehabilitation that would add upwards of 50 years to its useful life. In partnership with the City, SEH provided project management, preliminary design, public outreach, agency coordination and final design services. The team also provided construction support and drone filming to share progress with the public and stakeholders.
Simultaneous water main rehabilitation
Adding to the complexity of the 10th Avenue SE Bridge Rehabilitation, the City also replaced a large water main that was suspended underneath the bridge structure. More than 70 years old, the 54 in. water main suffered from many similar deteriorating conditions as the bridge.
SEH provided permitting and construction inspection services for this separate but simultaneous project. The water main was removed from beneath the bridge and a replacement installed underneath the river by excavating two large, deep shafts on both sides of the river. The project team did this by using a specialized tunneling machine.
Bridge design and rehabilitation
The SEH project team created detailed plans to remove the arch span segment concrete bridge deck and replace it with a brand-new deck. The majority of the team’s efforts involved designing and rehabilitating the seven main concrete arch spans of the bridge. This included removing deteriorated concrete, galvanizing in-place reinforcement, and adding new reinforcement and concrete to the repair location.
Elements of the arch spans repaired in this manner included the spandrel columns, spandrel cap beams and the arch ribs. A thermally sprayed metal anode system for cathodic protection was added to the tops of the arch ribs. This added an additional layer of protection to the in-place arch rib steel reinforcement that had been compromised from saltwater infiltration.
In addition, the project team rehabilitated two approach spans by milling off parts of concrete, replacing the spans with a new concrete overlay and removing and replacing the deck joints. The team added a 12 ft. sidewalk to the upstream side of the bridge; the downstream sidewalk was expanded from 10 ft. to 12 ft.; and a 2 ft. concrete median was added to provide protection between vehicular traffic and the bicycle lanes.
Sustainability and historic preservation
Sustainability played a prominent role in the 10th Avenue SE Bridge Rehabilitation. The SEH team designed a solution to strengthen the historic structure by keeping much of the bridge intact and replacing only what was necessary. Preserving and rehabilitating the bridge in this way saved and re-used an exceptional number of materials.
The design reduced the number of vehicular traffic lanes from four to two in order to accommodate expansion of the crossing’s bike path and a newly added walkway. Fewer traffic lanes and safe multimodal travel for those bicycling, walking and rolling will significantly reduce the City’s carbon footprint.
Adhering to the City’s budget
The City and SEH worked closely on the design, specifications and planning to ensure an accurate cost estimate. However, with expansive bridge rehabilitations, coming up with a precise cost estimate for construction bidding could have been difficult.
With little margin for error and the project being funded through State of Minnesota bonds and local bridge funding, the close collaboration, experienced and careful planning resulted in bids less than 1% from the original engineer’s estimate.
This supported the City’s ability to meet its initial budget projections.
Overall, the City and SEH team worked closely to achieve the City’s key objectives and restore its historic infrastructure in a way that will serve multimodal travelers for decades to come. The bridge was officially completed and fully open to all modes of traffic in November 2021.
10th Avenue SE Bridge Rehabilitation
City of Minneapolis
Olson & Nesvold Engineers; Genesis Structures; HDR; Hess, Roise and Company; HZ United; Beton Consulting Engineers; and Braun Intertec