The 18th Street Bridge – a continuous steel girder bridge carrying 3,000 vehicles each day – was originally constructed in 1962 and rehabilitated in 1982. During a routine inspection in May 2015, the deck, superstructure, and substructure earned ratings of serious condition (3 out of 9), fair condition (5 out of 9), and poor condition (4 out of 9), respectively. The deck had cracks, potholes, extensive delamination, and exposed rebar.
The sidewalks were in no better condition, with cracks, deep spalls, and voids at the southeast approach. The inspector also found severe concrete deterioration in the bridge’s abutments and heavy corrosion of the top and bottom flanges of the girders. Due to the serious outcome of the inspection, the bridge was considered a high priority points and was slated for a complete rehabilitation.
The new bridge deck has a five foot, four-inch overhang on both sides of the bridge for a new ADA-compliant sidewalk on each side of the bridge. To accommodate this width, an engineered falsework/bridge deck pour plan was utilized to form the overhang. During the deck pour, the bridge deck paving machine was unable to ride on this type of overhang system. Therefore, to carry the load, the bridge deck paving machine ran on temporary supports on the girders so the overhang would not be overloaded. The sidewalks were finished by hand, and the cross slopes were continuously checked to ensure compliance with ADA requirements.
To accommodate the public, the trail sections to be repaired were left in for as long as possible before reconstruction. There was additional significant acceleration at the end of the job so the trail section could be completed before the scheduled Coca-Cola Classic 5k, 10k, 1k, and Toddler Trot. This event is a part of the Missouri River Runners’ Organization and has been in existence since 1995. Hawkins Construction accelerated the work at its own cost so this popular annual event could still be held.
The project team utilized an innovative fall protection safety system at all times during the project. This Professional Engineer-stamped system for bridge decks is comprised of cables and metal panels under the bridge with safety gear that prevented a worker from falling more than a few feet if they were to fall from the bridge deck, which was 30 feet above the water below. At the same time, the safety system also prevented construction materials from falling into the water, thus providing an environmental advantage as well.
202,893 SF bridge deck (form and poured)
1,100 CY of concrete in bridge deck, bridge rail, and bridge approach
244,000 Lbs of rebar
25,000 Lbs of structural steel plates
14,000 tons of modified subbase material to stabilize existing failing approach sections
723 tons of bridge deck removal
101 tons of backwall and wing-wall removal
410 tons of bridge approach removal