A residual strength model for deteriorating post-tensioned concrete bridges

Inspection of UK's entire stock of post-tensioned concrete bridges of the i nternally grouted duct type has revealed a variety of defects. These includ e the presence of grout voids in incompletely grouted ducts, and chloride-i nduced tendon corrosion ranging from slight surface pitting to extensive lo calised corrosion and fractures. These defects may have a detrimental effec t on the load carrying capacity of such bridges but, to date, there have be en only limited attempts to provide satisfactory analytical methods to asse ss their residual strength. The lack of appropriate analytical tools may le ad to unnecessary strengthening and repair, or even costly replacement. This paper describes the development of an analytical model to assess the r esidual strength of deteriorating post-tensioned bridges. The model is a us eful tool in the investigation of the effects of tendon failure and regions of grout voids. A non-linear method of analysis is proposed, based on the concept of strain compatibility, but suitably modified to accommodate the b ehaviour of unbonded tendons in regions of incomplete grouting in the ducts . Also incorporated in the model is the contribution of failed tendons afte r re-anchoring into the grout. This uses the established phenomenon of re-a nchoring to estimate the distribution of residual prestress after tendon fa ilure, where both the distribution of grout voids along the beam and the qu ality of the grout are considered. The provision of such an analytical tool should be of considerable value to bridge engineers involved in the assess ment of corrosion-damaged posttensioned bridges, and will assist in the dev elopment of strategies for extending the lives of such structures through r epair and strengthening. (C) 2000 Elsevier Science Ltd. All rights reserved .