Assessment of deteriorating post-tensioned concrete bridges.

A non-linear analytical model was developed to assess the residual strength of deteriorating post-tensioned concrete bridges containing integral grouted tendons. The damage mechanisms addressed were those due to failure of the prestressing tendon as a result of corrosion, and the presence of grout voids within the ducts. The model was based principally on the method of strain compatibility, but modified to accommodate unbonded tendons in regions of incomplete grouting in the ducts. The phenomenon of tendon reanchoring was also incorporated to estimate the distribution of residual prestress after tendon failure. This considered the distribution of grout voids along the beam and the quality of the grout surrounding the tendon. Once validated, the model was used to study the effect of tendon failure and regions of ungrouted tendons on the residual structural capacity of typical bridge beams incorporating a variety of defects. It was found that the presence of voids within the re-anchoring length of failed tendons will affect the ability of the tendon to re-anchor fully and may affect the residual strength of the beam. The distribution of grout voids along the beam is thus an important factor when considering loss of strength. It was also demonstrated that significant levels of deterioration do not always compromise ultimate strength to a significant degree, hence avoiding the need for costly replacement. In addition to the global analysis of beam strength due to failed tendons, the local effect of partial loss of tendon area was investigated with ANSYS finite element software. This enabled the level of stress enhancement in the corroded tendon and the amount of loss of prestressing force to be determined. Valid bond models were established based on results from available field observations. It was found that only a relatively small amount of prestressing force is lost as a result of partial loss of area in a tendon in part due to the redistribution of force to adjacent tendons.