Impact of Partial Bridge Raising on Post-Tensioned Steel Plate Girder Bridge

The 1378-ft-long, 10-span continuous Kootenai River Bridge in Bonner's Ferry, Idaho is a rare example of composite design utilizing a prestressed concrete deck and steel plate girders. Through the use of transverse and longitudinal post-tensioning in the cast-in-place deck, a minimum girder spacing of 18 ft was achieved. Additionally, this structure was constructed in the early 1980's without any interior expansion joints, accommodating all longitudinal movement at the bridge ends via finger plate expansion joints. The functionality of the expansion joints and the condition of the bridge's pot bearings were investigated in 2004. Although the bridge superstructure and substructure were in satisfactory condition, some of the bearings required replacement as a result of deterioration due to exposure to the elements and leakage through the expansion joint. In order to facilitate removal and replacement of the deteriorated bearings, the superstructure required raising. It was infeasible to raise the entire bridge, requiring that the bridge be raised partially (i.e. differentially) which led to distortion of the bridge cross section. A series of finite element analyses were performed to investigate the stress changes and total stresses due to various bridge partial raising scenarios. Strengthening plans were subsequently developed for structural elements that would be subject to higher demands than their capacities. Where members could not be practically strengthened, analyses could be used as a tool to determine the allowable differential jacking heights. The finite element analyses also provided reactions at various supports, which were then used to develop requirements for jacks and jacking stiffeners. Construction was completed in 2008. This paper presents the analytical technique used to investigate the impact of partial raising on the composite post-tensioned concrete deck, steel plate girder bridge and discusses lessons learned during the course of design and construction.