ILDOT US 52 Savanna-Sabula Deck-Tied Arch Bridge Replacement
This project includes the replacement of a historic steel truss bridge and realignment of US 52 crossing the Mississippi River between Savanna, IL and Sabula, IA. The new 11-span bridge comprises three separate portions, two plate girder units consisting of 10 spans totaling 1,908 feet, and the central 546-foot-long tied-arch span, perched 60 feet above the main navigation channel. Web-plate girder depths range from 54-inches and 84-inches on the Iowa approach to 78-inches on the Illinois approach. The spans consist of a six-girder layout with girders spaced at 7.25-feet. The use of six girders allows for future deck replacements to be performed one-half at a time while enabling bi-directional traffic to be maintained during all maintenance and repair operations. Overall, the new structure features two 12-foot driving lanes with 8-foot shoulders. The project also involved the construction of a 1,565 foot-long soldier pile wall with aesthetic concrete cladding to facilitate the realigned Illinois Route 84 at the eastern end of the structure. Wall height ranged from 12 to 29 feet.
Using an alternative to the original design, we erected the tied arch with contractor-designed towers and an onsite cantilevered method of erection. This innovative alternative minimized the impact on marine navigation and recreational boat traffic by eliminating the need to construct in-water falsework adjacent to active shipping lanes by using a multi-staged construction erection plan. Through this method, bridge pieces were transported by a barge, where a crane was used to install the arch pieces in place, supported from cable-stays above. In preparing for the erection sequences, we performed the in-depth structural analysis at each stage to ensure we did not exceed the allowable stress. A temporary falsework system and multi-strand stay system was then installed to facilitate suspending 3,000,000 pounds of structural steel for the tied-arch during the erection. This adjustable system allowed the project team to maintain geometry and steel stresses within allowable limits throughout construction to perform gradual tensioning and de-tensioning of 19 strand stays. We used an automatic surveying system that measured the work points of the arch erection geometry plan on an hourly basis—24 hours a day, seven days a week—with continuous measurements in real-time during segment erection. By maintaining rigorous geometry control, both erected cantilevers were able to meet in free-space without incident. Through these innovative techniques and expertise with complex steel erection, we opened this bridge to traffic, meeting the owner’s tight timeline and seamlessly maintaining the transportation connection between Illinois and Iowa.