Assessment and rehabilitation of FC girder bridges

Almost two hundred precast prestressed FC girder bridges were built in the province of Alberta over a twenty year period from 1960 to 1980. Many of these bridges have required rehabilitation due to the deterioration and failure of the field grouted longitudinal shear keys between the girders. Many rehabilitation schemes have been tried by Alberta Transportation in the past, but none have successfully rectified the problem. No thorough study has been carried out on monitoring the field performance of these structures and most bridge reviews are based on visual inspections that focus on the appearance of alarming signs.; This research program was designed to investigate and better understand the behaviour of FC girder bridges by conducting a three fold research program. The first part consisted of an extensive field survey meant to review the current condition of these bridges, visually assess severity of the field problem and verify shear key cracking concerns. While the second part constituted field testing and assessment of FC girder bridges to observe load sharing concerns as well as the response of the bridge to service loads. Load and vibration testing was conducted to measure deflections, strains and natural frequencies and mode shapes of the bridges. All the test measurements complemented each other and indicated partial load sharing between the girders as a result of shear key cracking.; The third and final phase of this research consisted of the development of a finite element model based on results from the field tests. A comparative study of the performance of the different rehabilitation schemes, in the finite element model, indicated that all rehabilitation strategies improved load sharing among the girders. However, a combination of transverse prestressing and transverse steel underslung diaphragms was the best rehabilitation technique to avoid future shear key cracking. Differential movement at shear key joints in the form of deflections and rotations generally accelerate shear key cracking and must be arrested by increasing the stiffness of the transverse span. The success of the proposed scheme lies in its ability to transform the transverse cross section into a stiff plate hence eliminating all differential movement at the shear key lines.