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

Reviews a recently proposed predictive model that projects the onset and subsequent rate of wire and strand fractures and tendon failures as a function of time. Includes first fracture onset results for wires and strands, failure onset for tendons, failure rates and testing of simulated tendons.

Product Number: 51317--8828-SG
ISBN: 8828 2017 CP
Author: William Hartt
Publication Date: 2017
Industry: Highways & Bridges
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Onset and Subsequent Failure Rate of Corroding Post-Tension Tendons with Deficient Grout – Effect of Modeling VariablesPost-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 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. In response to this a recently proposed predictive model that projects the onset and subsequent rate of wire and strand fractures and tendon failures as a function of time is reviewed along with results from testing of simulated tendons that support the approach. Inputs to the model are the mean and standard deviation of first depth of localized corrosion on wires and second the corresponding fracture stress both of which were shown to be normally distributed. The present paper reviews this modeling effort including first fracture onset results for wires and strands and failure onset for tendons and second subsequent fracture and failure rates. Specific focus in the present effort is upon the effect of material tendon and analysis variables on model projections. These variables include the following:Strand/tendon stressWire/strand strengthModeling random number sequenceNumber of tendons andTendon length.Results are discussed with regard to integrity and failure projection of corroding PT tendon systems.

Key words: Post-tensioning, corrosion, bridges, grout, deficiencies, fracture, failure.

Onset and Subsequent Failure Rate of Corroding Post-Tension Tendons with Deficient Grout – Effect of Modeling VariablesPost-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 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. In response to this a recently proposed predictive model that projects the onset and subsequent rate of wire and strand fractures and tendon failures as a function of time is reviewed along with results from testing of simulated tendons that support the approach. Inputs to the model are the mean and standard deviation of first depth of localized corrosion on wires and second the corresponding fracture stress both of which were shown to be normally distributed. The present paper reviews this modeling effort including first fracture onset results for wires and strands and failure onset for tendons and second subsequent fracture and failure rates. Specific focus in the present effort is upon the effect of material tendon and analysis variables on model projections. These variables include the following:Strand/tendon stressWire/strand strengthModeling random number sequenceNumber of tendons andTendon length.Results are discussed with regard to integrity and failure projection of corroding PT tendon systems.

Key words: Post-tensioning, corrosion, bridges, grout, deficiencies, fracture, failure.

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