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EFFECT OF MODELING VARIABLES UPON PROJECTION OF CORROSION INDUCED POST-TENSION TENDON FAILURES

The present paper reports results of analyses that address the influence of physical and modeling variables upon failure projections.

Product Number: 51318-10496-SG
Author: William H. Hartt
Publication Date: 2018
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Post-tensioning (PT) has become an important technology 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 but 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 concentration 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 methodology has been developed whereby timing of an initial wire and strand fractures and tendon failure can be projected and then rate of subsequent fractures/failures, given information regarding wire corrosion statistics; and a degree of verification was provided based upon results from mockup tendon exposures and forensic analyses of a failed bridge tendon. The present paper reports results of analyses that address the influence of physical and modeling variables upon failure projections. These include the following:

1. Analysis variables (generation of random numbers)

2. Strand/tendon stress,

3. Wire/strand strength,

4. Number of tendons, and

5. Tendon length.

The significance of each is discussed and results are related to the timing of tendon failures on bridge structures.

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

Post-tensioning (PT) has become an important technology 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 but 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 concentration 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 methodology has been developed whereby timing of an initial wire and strand fractures and tendon failure can be projected and then rate of subsequent fractures/failures, given information regarding wire corrosion statistics; and a degree of verification was provided based upon results from mockup tendon exposures and forensic analyses of a failed bridge tendon. The present paper reports results of analyses that address the influence of physical and modeling variables upon failure projections. These include the following:

1. Analysis variables (generation of random numbers)

2. Strand/tendon stress,

3. Wire/strand strength,

4. Number of tendons, and

5. Tendon length.

The significance of each is discussed and results are related to the timing of tendon failures on bridge structures.

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

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