Keystone Bridge Rehabilitation | Projects Origin Design

The Origin Design team worked with the City of Elkader, Iowa Department of Transportation (DOT) and State Historical Preservation Office (SHPO) to allow the Keystone Bridge to remain an Elkader landmark.

Built in 1889, the structure, featuring two 90’ limestone arches, is on the National Register of Historic Places. When funding administered through the DOT became available for structure rehabilitation, the City selected Origin Design to help the community through the process. The funding is federal-aid Competitive Highway Bridge Funding Program (BHM-CHBP-2315(607)--NA-22) and SWAP funded Urban Bridge funds.

Origin Design worked closely with Atkinson-Noland & Associates, Inc., a sub-consultant specializing in limestone bridge structures, to help determine the potential bridge strengthening options. Extensive coordination was needed with the Iowa DOT to meet SHPO requirements since the historic Elkader downtown is also on the National Register of Historic Places. Initial consultation with the IDOT eliminated some walkway options due to the requirement of a “no adverse effect” determination to keep the project eligible for the CHBP funding. Design criteria was evaluated. It was determinedthat the structure didn’t need to meet full legal weight loading requirements — it would need to meet an allowable loading of H15 would meet requirements.

The pedestrian walkway is a cantilevered structure. The intent is to replace the existing walkway entirely and create a walkway with a minimum width of 6’. The structural analysis needed to consider not only the capacity of the steel beam supports, but also the connections. Due to federal funding, a structural calculation packet was submitted to the Iowa DOT for review. Constructability was a key consideration because of the existing bridge load restrictions and the existing pedestrian walkway tie rods and estimated location of the top of the roadway limestone arch. The proposed design worked around these constraints.

Since the walkway is being replaced, in order to communicate with both the City and SHPO, renderings were created. The renderings illustrated the scale and color of the proposed walkway railing and substructure and were used to obtain concurrence from SHPO that the proposed walkway is consistent with the aesthetics of the structure. In addition to the replacement of the walkway, the bridge deck is being replaced with a reinforced concrete deck and drainage system to reduce the potential for saltwater to further damage the limestone. Details for various limestone repairs and strengthening were incorporated into the plan set.

The project required a floodplain permit from the Iowa DNR, however since the proposed work is being performed on the existing structure, a hydraulic analysis was not needed for the permit submittal.

The State Historical Society of Iowa Board of Trustees selected the City of Elkader as the recipient of the 2024 Excellence in Archaeology and Historic Preservation Award for the Keystone Bridge Rehabilitation project.