Influence of partial bond and degradation on posttensioned prestressed girders

Abstract

Prestressed beams with post-tensioned tendons in existing bridges often exhibit a state of degradation due to an initial deficit in the grouting of the sheaths, which frequently leads to corrosion of the internal prestressed reinforcement. This defect often remains hidden, and, in some cases, it was fatal due to severe corrosion. In most cases, however, incomplete grouting of the sheaths results in a partial loss of bond in some areas, rather than total debonding, along with zones of varying degrees of corrosion degradation along the length of the tendons. In the literature, the loss of bond, which can also result from corrosion-induced strand degradation, is generally considered by assuming that the stress on the strands remains almost constant, until the Ultimate Limit State. Experimental evidence and inspection experiences of existing bridges suggest that the partial presence of the bond might induce the tendon to resist with an increased tension compared to the service load, maintaining the characteristic behaviour of an internal tendon. This study presents a few scenarios involving prestressed beams with post-tensioned with partial bonded tendons and related numerical analyses that allow for a better understanding of the actual behavior of the post-tensioned girder.