DSI USA Strengthens I-39/Kishwaukee River Bridge in Illinois
The Kishwaukee River Bridge is part of Interstate I-39, which crosses the US-American state of Illinois from North to South. I-39 is especially frequented on weekends by Chicago residents who spend their weekends in Wisconsin.
The Kishwaukee River Bridge consists of two separate bridge structures, one for each direction of travel, over the Kishwaukee River near Rockford.
The double bridge consists of two precast segmental concrete bridges opened to traffic in 1980. Each bridge has five spans with lengths of 170ft + 3 x 250ft+170ft (51.8m+3 x 76.2m + 51.8m). Since the double bridge belongs to the first generation of segmental structures, the responsible engineers chose the design of a single shearkey joint usually located close to the centroid of the cross-section.
Both bridge decks have an overall length of approximately 332m (1096ft) and were built using the balanced cantilever method. Each cantilever consists of 17 segments approximately 2.2m (7’-3/5") long and one pier segment approximately 1m (3’-6") long. Cast-in-place closures have a length just short of 1m (3’-2 3/4"). During the construction of the bridge at the end of the 70s, DSI USA used the special DYWIDAG THREADBAR® system instead of the post-tensioning system that had been part of the original plans.
At the beginning of the new century, the owner of the bridge, the Illinois Department of Transportation (IDOT), decided on a strengthening program to extend the design life of both bridge structures. The strengthening design developed by Parsons Transportation Group required an addition of a total of 24 12x0.6" external Post-Tensioning Tendons of various lengths in each bridge.
The contract for the strengthening of the bridges was awarded to the same team as 28 years previously: Edward Kramer & Sons again subcontracted with DSI to supply and install the post-tensioning. The special challenge during this project was the fact that all work needed to be completed within a very short time schedule in order to obstruct the traffic flow as little as possible.
In the 1970’s, design practice did not require the inclusion of provisions for future additional post-tensioning tendons. Therefore, new tendon deviators had to be constructed throughout both bridges as well as new post-tensioning anchorage zones at the diaphragms and abutments. The new anchor zones and deviators were cast in place within the segmental box and then post-tensioned.
Instead of using traditional steel pipes in the deviators, continuously curved voids (diablos) were cast in the deviation diapraghm to allow large deviations from the theoretical tendon profile. According to recent technical standards, the post-tensioning was designed with a continuous air tight HDPE pipe from anchor to anchor grouted with high performance grout and equipment. Due to the diablos and continuous HDPE pipe requirements, specially designed post-tensioning anchors were installed at the faces of the existing diapraghms. The location of the new anchors was made difficult by the tight constraints of the existing reinforcement and post-tensioning.
All parties worked very closely together throughout the project due to the complex 3D geometry and challenges of accommodating the tendon paths throughout the existing bridges. In order to locate existing post-tensioning and reinforcing in the diapraghms and abutments, ground penetrating radar (GPR) was used.Thus, crews could follow closely behind with coring of the holes for the tendon paths. After casting, the new anchors and the HDPE pipes were successfully installed.
The work was made difficult by the largely deviated tendon paths and tendons lengths of over 770ft (235m). In addition, the tendon stressing was difficult due to the location of the tendons in the upper corners of the box, along with the congestion of the new tendons and new anchors.
The southbound bridge was completed in May 2008 and the northbound portion of the project was succesfully completed in early August 2008, with final project completion coming within the owner’s short-term schedule.