Modeling and Projecting the Onset and Subsequent Failure Rate of Corroding Bridge Post-Tension Tendons

摘要

Post-tensioned (PT) concrete construction was first introduced over 60 years ago and has evolved to become a prime methodology for affecting integrity of large reinforced concrete structures, including bridges. While there are a number of advantages to PT construction compared to conventional reinforcement, corrosion caused tendon failures have recently been reported, in some cases within a few years of construction, as a consequence of either chemically or physically deficient grout (or a combination of the two), where the former involves elevated concentrations of chlorides or free sulfates (or both) and the latter voids with free water, and soft, chalky, segregated, separated grout. The present paper reviews a predictive model that was developed to project the onset and subsequent rate of wire and strand fractures and tendon failures as a function of time, given information regarding the present extent of corrosion. Inputs to the model are the mean and standard deviation of, first, remaining cross section area at the most corroded location on individual wires and, second, an experimentally determined relationship between fracture stress and remaining cross section area of corroded wires, both of which are represented as distributions. Particular emphasis is placed upon fracture and failure rates subsequent to first occurrence, since these can provide useful information for assuring timely intervention and integrity assurance of PT structures with corrosion issues. The results indicate that tendon failures, once initiated, can become unmanageable even for relatively modest rates of corrosion.