HENNEPIN COUNTY FRANKLIN AVENUE BRIDGE
OVERVIEW
The Franklin Avenue Bridge is a 1055-foot-long, five-span, open concrete deck, arch structure that opened as a vital link over the Mississippi in 1923 (placed on the National Historic Register in 1978). The bridge underwent a major rehabilitation in 1970, which removed historic elements that Kraemer partially restored as part of this project. Kraemer used accelerated bridge construction (ABC) techniques and precast elements (cap beams, bridge deck, ornamental railing) to remove/replace 47 spandrel/pier cap beams and 72,000 SF of bridge deck in a compressed 116-day full closure. Work included substructure surface repairs and repairs to two cofferdams. Kraemer worked with the owner before full closure to develop a precise removal and erection sequence that minimized movement/unwanted stresses within the arch ribs.
INNOVATIONS
Extensive field engineering was required to overcome associated and unforeseen challenges. One major challenge was precisely fitting all precast elements to the existing bridge first constructed 100 years ago. Kraemer conducted a comprehensive plans and site conditions survey and discovered that most of the existing cap beams, columns, and piers were not detailed in the 1923/1970 drawings. The project team worked quickly to survey and modify the overall geometry to maintain the highest structural integrity and achieve proper substructure alignment. The owner verified Kraemer’s geometry and approved its use for shop drawing development and the designer provided an onsite structural engineer to review shop drawings for acceptance in real-time so drawings could be incorporated into the fabrication process immediately. The timing of verification and approvals was critical because no two precast deck panels of the total 360 were identical. The 116-day full closure would not have been possible without the effective/efficient team work the entire project team displayed throughout the ongoing precast fabrication process.