CMAR Collaboration to Design the Longest Steel Girder Span in Arizona

Virgin River Bridge No. 1 carries travellers across the scenic Virgin River on Interstate 15 in the northwest corner of Arizona. The Arizona Department of Transportation began the process of replacing the existing bridge in 2012, and HDR was retained in 2018 to provide final design services as part of a construction manager at-risk contract.

HDR provided final bridge design, geotechnical services, utility coordination and more. When complete, the $57 million project will feature the longest steel girder span in Arizona.

A CMAR Approach to Replacing Existing Bridge

Built in 1964, the existing Virgin River Bridge No. 1 is a five-span haunched steel girder bridge with a long history of repairs and replacements that has reached the end of its service life.

After the last repair project in 2012, ADOT initiated a scoping phase to determine the long-term approach for this crossing. Two major findings came out of this process, which lasted from 2012-2018: replace the bridge on the same alignment; and utilize the CMAR delivery method.

In early 2018, HDR was retained to provide final design services. In early 2019, after the 30% design package was complete, Kiewit was retained as the CMAR contractor. The design phase concluded at the end of 2020 and construction began in February 2021. The new bridge is scheduled to be completed in 2023.

Design Challenges

Replacing the five-span existing bridge will be a three-span structure — 240 feet, 360 feet, 240 feet. The design minimizes risk associated with pier foundation work in the river where deep foundations are required to be designed for nearly 70 feet of scour, anticipating a 500-year extreme flood event.

One of the major project challenges is replacing the bridge in the same location while maintaining traffic. The new bridge needed to be constructed within the limits of the existing bridge, as cultural resources on the west end of the bridge could not be disturbed and maintaining the same profile was desired to limit the amount of approach roadway work. The solution was to use staged construction, but it required crafting a design with tight geometric constraints, both horizontal and vertical.

Collaboration Success

Collaborating with the contractor during design through the CMAR delivery method provided the opportunity to improve constructability and accommodate the contractor’s preferred means and methods for replacing the bridge. Several major elements of the bridge layout and design were influenced by the CMAR delivery process, including the span configuration, horizontal alignment, pier drilled shaft construction and more.

For example, the proposed structure evolved from a five-span haunched weathering steel plate girder bridge to a three-span haunched weathering steel plate girder bridge. Replacing a five-span bridge with another five-span bridge in the same location created unbalanced spans to avoid existing pile foundations left in place. To achieve a more balanced span arrangement and efficient girder design, our design team initially developed a four-span bridge. Working with the contractor, however, a three-span option was eventually chosen to minimize risk associated with pier foundation work in the river.

Keeping Commerce Moving

I-15 is an essential trade route and part of the Canamex corridor established by the North American Free Trade Agreement, linking Canada to Mexico through the U.S. As such, it plays a critical role in delivering goods across the region. Keeping trucks moving is critical, as detours in the event of a closure range from 250 miles for commercial trucks to 600 miles for oversized loads. The replacement of Virgin River Bridge No. 1 will ensure the regional corridor can safely continue carrying commerce for decades to come.