NO. 4 BRIDGE: 8th Street Bridge Rehabilitation and Greenway Improvements

Rehabilitation of a historic structure while maintaining its original identity was a challenge for the City of Sioux Falls, South Dakota.

Initial phases of the 8th Street Bridge rehab project consisted of an in-depth inspection of the structure to quantify areas of deterioration, re-create existing plans of the structure for load rating analysis, analyze existing concrete characteristics through coring and petrographic analysis, conduct historical research, and provide a summary of findings with recommendations. At over 100 years old, deterioration was prevalent throughout the structure. The most significant amounts of deterioration were located on the underside of the arches within the outer 10 ft on the north and south edges of the bridge. Reinforcement was exposed and showed 70% section loss. The bridge had experienced some significant deterioration.

There were no design plans from the original structure for the 8th Street Bridge. The design team needed to complete testing of the in-place concrete and steel to determine viability of rehab. After the testing phase, rehabilitation was determined to be viable and cost effective versus removal and replacement of the structure.

The 8th Street arch bridge is part of the city’s vision for the Big Sioux River greenway. The bridge is located in downtown Sioux Falls and has developed buildings and businesses on all corners of the structure. This presented access and constructability challenges. A temporary causeway was constructed and phased to provide access to all portions of the arch. The temporary causeway was designed, permitted, and included within the construction documents allowing construction to occur without environmentally related delays.

The city’s downtown 60-in.-diam. sanitary sewer trunk line runs parallel to the river and under the east span of the structure. Construction of the greenway improvements, including river walls, could only be completed in small segments to avoid exposing more than one sanitary sewer pipe joint at a time.

One important element of the preliminary design stage was defining the final aesthetics of the bridge and river greenway. The consensus included a focus on keeping the current and original aesthetics of the bridge. Additional elements to be added to or around the bridge were focused on enhancing the bridge architecture but not steal the focal point from the bridge itself. The goal was to make the bridge look similar in architecture when completed but also include enhancements such as balustrade lighting and up-lighting of the arches. Existing plaques were also reincorporated in the bridge. The third lane located on the existing bridge would be removed to allow for extra width of the pedestrian pathways. Balustrade railings were replaced with replica precast balustrade railings.

Final project elements included greenway improvements on both sides of the river, an interpretive wall display along the west trail under the bridge, hydrodemolition and traditional concrete removal, surfacing and bridge fill removal, water proofing of the arches, color matched and hand stamping of shotcrete repairs, resurfacing of the spandrel walls, pier nosing reconstruction, new bridge drainage system, precast balustrade railings, historic street lighting, balustrade railing lighting, up-lighting of all arches, river greenway walls, water main and utility installation, and final concrete surfacing.

“The City of Sioux Falls made the decision to rehabilitate the 8th Street Bridge after extensive analysis with our project partners,” Mark Cotter, P.E., Director of Public Works for the City of Sioux Falls, told Roads & Bridges. “We are proud of this historic bridge that is over 100 years old has been fully rehabilitated and will serve the pedestrian and transportation needs of downtown Sioux Falls for the next 75 years.”

The project began in early March of 2020 with construction of the temporary causeways providing access to the underside of the arches. Surfacing removals on top of the bridge began immediately to allow time for concrete encasement removal, consolidation of fiber lines, and construction of the cable-stay support system.