Bridge Upgrades Preserve Historic Structure
Originally constructed in 1912 with only minor modifications in the intervening years, the iconic Eureka Bridge in central Iowa has been listed on the National Register of Historic Places since 1992 as part of the original Lincoln Highway. Spanning the North Raccoon River just west of the City of Jefferson, this historically significant structure consisted of a five-span, concrete arch bridge with closed-spandrel, earth-filled arches.
Greene County officials were faced with the decision of either replacing this bridge or finding an engineering firm capable of designing rehabilitation measures that would preserve the integrity of the structure while meeting current bridge and highway design standards. After a difficult decision-making process, the Greene County Board of Supervisors and Greene County Engineer chose Shuck-Britson to design the bridge upgrades and parent company, Snyder & Associates to design the roadway approach.
Bridge Rehabilitation Efforts Retain Iconic Charm
The primary concern with the existing bridge was the narrow deck that no longer met the minimum requirements for a highway bridge. Our design team opted to widen the bridge’s deck to the south by extending the existing abutments and piers. This was accomplished by driving long steel pilings deep into the earth to extend the original pilings. These pilings were then able to support the new abutments, piers, and the bridge’s superstructure. The south spandrel wall and concrete rail were constructed to replicate the original construction. Widening the bridge deck to the south also alleviated certain road alignment and right-of-way issues.
Our team’s extensive engineering analysis also focused on the earth-filled superstructure of the original bridge. This analysis determined that an alternate deck support system would increase the live load capacity of the bridge. As a result, the rehabilitation project removed the fill and the concrete deck that it supported and added concrete transverse walls to support a new deck. The earth-fill removed from the bridge was able to be repurposed on the west bank of the river where it formed roadway access to a county park.
The balustrade-design poured concrete guardrails on both sides of the bridge deck were of particular concern for maintaining the bridge’s appearance. Because the deck was widened to the south, the north side of the bridge was left unchanged and the entire north spandrel wall and guardrail were protected and left in place. For the south guardrail, the team decided to replicate the bridge’s original panel-designed, poured concrete guardrail. To comply with highway crash standards, new “transparent” steel traffic rails were built to protect the historic concrete rails according to current design load and geometry requirements. These two-foot-high guardrails were designed so as not to interfere with the exterior view of the bridge.
Roadway Conditions Improved with Additional Modifications
Designing the bridge went hand-in-hand with an analysis of roadway conditions. The road needed to be brought up to current design standards and several alignment adjustments were analyzed within the existing roadway constraints to devise a solution to this challenge. This analysis resulted in the modification of roadway curves, the bridge’s increased width, and the addition of the steel guardrails.
All planning, design, and construction were coordinated by the Shuck-Britson and Snyder & Associates design teams with the Iowa Department of Transportation (DOT), the State Historical Society of Iowa, and Greene County officials. This rehabilitation, while preserving a vanishing piece of Iowa history, will now continue to serve motorists for decades to come.