Transportation landmark

EXP designs a regional gateway for Meredosia, Ill., linking the community to a new bridge over the Illinois River

By Nadia Abou and Sarah Wilkinson, CPSM

In June 2018, the small rural community of Meredosia, located 60 miles west of Springfield, Ill., welcomed the opening of the new IL-104 Bridge over the Illinois River. Local residents and community leaders waited for the unveiling of the structure that would serve as a new gateway for the region and replace the previous bridge built in 1936. Replacing the existing 75-year-old, structurally deficient and functionally obsolete bridge was paramount to economic growth and regional mobility.   

EXP challenged traditional design approaches to find a comprehensive solution for the bridge. The crossing of IL-104 over the Illinois River served as a backbone to the region’s transportation networks and was critical to the region’s economy. Closure would, in fact, cause major impacts to the region. At the same time, any replacement structure needed to be efficient, economical, and easy to construct. Led by the Illinois Department of Transportation (IDOT), EXP’s team determined how existing concerns over placement of the structure could be resolved with innovative planning and design solutions.

The team completed a preliminary engineering study, Environmental Assessment (EA), as well as final design for the bridge’s replacement using IDOT’s Context Sensitive Solutions (CSS) approach to yield the prevailing solution. A Bridge Type Study assessed possible bridge types for a new structure, including truss, cable-stayed, and tied arch. In total, 17 alternatives were evaluated, including rehabilitation of the existing 75-year-old bridge, reconstruction on the existing alignment, and a new bridge on a new alignment.

The outcome resulted in a replacement bridge located approximately 255 feet north of the existing bridge, minimally impacting traffic routes and commerce during construction. The new aligned bridge was purposefully selected because it would minimally impact acreage and farmland, cost less, and was supported by the local community and municipality.

The selected design for the new IL-104 bridge was a tied arch structure, meeting the project’s and client’s fundamental purpose of providing a reliable and secure crossing over the Illinois River for the next 100 years. EXP, IDOT, constructors, consultants, and steel fabricators all contributed to the thoughtful detailing in the new crossing. The design, which simultaneously struck efficient and economical cords by reducing inspection and maintenance costs, additionally required attention to stormwater and drainage to alleviate potential flooding.

While Meredosia’s downtown area is protected from rising Illinois River water by an uncertified levee system, the town still lies within a floodplain. EXP worked with IDOT and local town officials to integrate the revised river crossing within the downtown street grid and designed a pump station to discharge flood waters to the river. This collaborative and direct approach to planning and design yielded the most efficient and strategic result, presenting Meredosia and the region with a new tied arch bridge.

A new arch over the Illinois River

The new bridge spans 2,125 feet across the Illinois River with a 590-foot-long tied arch main navigation span and nine welded plate girder approach spans ranging from 142 feet to 200 feet. While tied arch bridges follow a standard design method, EXP utilized innovative processes to design the IL-104 Bridge. Innovative solutions included the use of I-sections tie girders to be more economical and easier to maintain, a design for high vessel-collision loads, seismic design for 2,500-year Return Period in Seismic Performance Zone 2, and seismic analysis performed by a 3D elastic model of the entire bridge.

Additional innovative highlights exceeding standard methods include simple floor beam to tie girder connections, Vierendeel arch rib bracing with large strut spacing and struts offset from the hanger locations, verification of aerodynamic stability by computational fluid dynamics modeling, and wind tunnel testing. IL-104 also features unbalanced dead load conditions not called for by any bridge codes, including AASHTO, and arch modeling and analysis using the state-of-the-art LARSA-4D Finite Element Analysis program. While many may just notice its distinctive blue arch, IL-104 offers a simple and unequivocal approach to steel detailing and design principles.

Revitalizing the community

The community played an influential role in the planning and design phase of the new crossing. During each phase, our team held public meetings with community members, agencies, and businesses, and utilized newsletters and a website to provide information on impacts to the village and the region. Coordinated efforts were ongoing with 10 federal and state agencies and 14 Native American Tribes, all while ensuring the needs of the local community would still be simultaneously met.

Residents and business owners thought a bridge closure would require a detour, causing traffic to be diverted, bypassing the Village of Meredosia. A closure would impact the region economically, disrupt commercial traffic routes and farmers, who regularly transport heavy equipment. After receiving community feedback and reviewing the completed EA and CSS, the tied arch bridge was built on a new alignment that still enabled traffic to run through the town, eliminating economic impacts.

The IL-104 bridge emerged to safeguard and enhance the region’s existing transportation and mobility network. Alongside IDOT, contractors, consultants, and an engaged community, EXP was able to create a transportation landmark to replace a structurally deficient and obsolete bridge. Today, a gateway stands as an iconic landmark of mobility, growth, and hope for the Village of Meredosia and the region.

Nadia Abou, corporate communications coordinator for EXP (www.exp.com), strives to enhance the public’s understanding of complex engineering projects and the array of benefits they provide to communities. Sarah Wilkinson, CPSM, director, corporate marketing at EXP, is passionate about the AEC industry and has spent the last 15-plus years thinking creatively about the built environment.