The original Rock Island Swing Bridge over the Mississippi River was built in 1894 and served the railroad on the upper deck and vehicular traffic as a toll road on the lower deck. The swing portion was removed several years ago and the City acquired the bridge along with a grant to repair part of the existing structure. They also added two new spans in order to create a pier overlooking the River.
Two weathering steel Continental® truss bridges, 250’ x 12.5’ and 140’ x 12.5’ in size, were chosen for their ability to match the look of the existing structure. In order to match the top and bottom chords of the new structure to the existing structure, a tall, through truss with support legs was needed. Due to the larger truss and legs, shipping became a challenge and needed to be monitored throughout the design process.
Additional challenges occurred during installation. First, the area received a record amount of flooding in the fall, delaying delivery and installation. Also, due to the long span length and the need for installation over the wide river, Lametti needed to used their marine group, L & S Marine, to place the 140 foot span utilizing a river barge. They used cribbing to lift the bridge close to the proper height and then filled the barge with ballast water in order to lower it to the proper location so that the bridge could sit on the piers.
“The Lametti staff and Contech were ingenious in their solutions to meet the truss shipping and erection challenges,” stated Jeff Johnson, Project Manager with SEH, Inc.
The 250 foot span consisted of five 50-foot long segments which were then transported with two large cranes into place. After both spans were installed, the crews began welding brackets into place to attach the decorative safety railing. Future plans include developing the surrounding area into a park-like setting called Heritage Village Park that will connect to the county regional trail system.
“The two new fabricated structures will help the public interpret the bridge not only by connecting people to the two existing structures but also through their construction methods and the design looking similar to the structures they replaced,” concluded Eric Carlson, Parks and Recreation Director with Inver Grove Heights Park & Recreation.