Keystone Connection a Success on First of Two I-74 Arches

QUAD CITIES, IA – On the morning of Wednesday May 6, 2020, the I-74 Mississippi River bridge team lifted a critical project component more than 200 feet into the air from a barge below. That component—called the keystone—connects four separate 400-foot-long ribs that make up one of two arches as part of a new signature river crossing. Work continued through the weekend as ironworkers adjusted the connection and secured the keystone with thousands of bolts, signifying a major milestone for the Iowa Department of Transportation (lead agency), Illinois Department of Transportation, and other project partners.

Crews worked for several days to fit the keystone into place more than 200 feet above the Mississippi River.

Spanning 800 feet, the new arch (and its soon-to-be-built twin) makes up only a portion the future 3,400-foot river crossing and is one of 25 structures to be built as part of this $1.2 billion I-74 corridor improvement. The project represents a joint effort between the Iowa and Illinois Departments of Transportation to bring much needed congestion relief to the ever-expanding Quad Cities of Moline, Bettendorf, Rock Island and Davenport—and it marks the Iowa DOT’s largest transportation project ever.

Traffic continues through the construction site on the original I-74 bridge (right).

Opened to the public in 1935, the original I-74 Mississippi River bridge was designed to accommodate 48,000 vehicles per day. Today, an average daily traffic count of 80,000 (with an expected increase to 100,000 in the next ten years) necessitated the structure’s replacement.

The existing structure carries only two lanes of traffic in each direction with no shoulder. When complete, the new crossing will provide four lanes in each direction in addition to a multi-use path connecting both sides of the river to existing trail networks.

The design for the new 3,400-foot crossing involved multiple consultants. Benesch designed the approach spans and led the substructure and foundation design of the main span. Modjeski and Masters led the design of the steel arches.
With four lanes in each direction, the new bridge will bring the capacity needed to support continued growth in the Quad Cities for decades to come.

The entire I-74 corridor improvement spans more than seven miles. In addition to its 25 new bridges, the completed corridor will also feature six reconfigured interchanges, 12 retaining walls, widened and reconstructed interstate roadway, and several miles of arterial roadway improvements.  

With so many components under construction to complete the corridor, the 800-foot arch is the most complex piece of this $1.2 billion puzzle—which is why the past week’s work has been so crucial.

In making the connection, ironworkers had to align the keystone piece with four separate and relatively independent arch ribs. Maintaining precise control of the keystone during the procedure was paramount, and no small feat at more than 200 feet above the river. Once relatively in place, there were over 1,000 bolts at each of the four rib connections that had to align to make the connection successful.  The contractor developed unique tools to push and pull the arch sections to achieve the required position and make the connection. 

Successfully connecting the keystone required custom tools for pushing and pulling the independent arch sections into place to align more than 4,000 bolts.

Benesch has played a significant role in this project since 2009, leading design plans for both the north and central sections of the new corridor, in addition to serving as the Corridor-Wide Coordinator on behalf of the Iowa and Illinois DOTs.

Since the start of construction in 2017, the project has generated more than 1,700 local jobs in the Quad Cities area. The westbound improvements are expected to be complete in 2020 with eastbound following one year later.