A parametric study on the effect of post-tensioning in bridge pier foundations

In this study, the effect of post-tensioning on a bridge pier foundation of a two span bridge was investigated by finite element analyses. For this purpose, a formerly constructed real bridge was selected and the pier foundation of this bridge was analysed for three different post-tensioning tendons and for three different tendon spacings making a total of nine different cases. The results were compared in the meaning of maximum and minimum base pressures, base pressure distributions; bending moments and their distributions at six different cross-sections in the longitudinal and transverse directions. The results have revealed that; without post-tensioning a significant pressure concentration was observed beneath the columns. While much more uniform base pressure distributions were obtained for most of the post-tensioned foundations at the expense of increased base pressures at the edges of the foundation. This fact was expected since the total vertical force was not changed but the deformation profile of the foundation was improved with the help of post-tensioning. Similar to the case in base pressures, moment distributions were also more uniform for most of the cases with post-tensioning. But after an optimum point for tendon type and spacing, the moment directions were altered which may have a diverse affect in the design. Another advantage of the application of post-tensioning was that the whole foundation was under compression which had a positive effect on the long term behaviour of bridge foundations against cracking and corrosion.