Predicting Residual Tensile Strength of Seven-Wire Strands Using That of Single Wires Exposed to Chloride Environments
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The steel strands in posttensioned (PT) concrete systems are typically embedded inside cementitious grout for protection from the environment. However, strands not embedded in grout have been observed in PT systems. The exposed strand is susceptible to corrosion, and particularly the location where the strand protrudes from the grout (i.e., grout-air-steel interface) is more vulnerable to corrosion. Prediction of the tension capacity (CT ) of strands with such interfaces under various exposure conditions is necessary for structural assessment. This prediction could be accomplished by using the data from an experimental program that includes the exposure of strands to various corrosive environments and testing to determine the time-variant residual CT of these strands. However, these tests are cumbersome and expensive, especially when it is necessary to maintain very high tensile stress conditions during the exposure period to simulate the in-service stress conditions on the strands in PT systems. Similar investigations of unstressed single wires are simpler and less expensive. This paper presents an experimental investigation of the corrosion-induced losses in the CT of unstressed wires, unstressed strands, and stressed strands. Based on these data, this paper develops probabilistic models to predict the CT of unstressed wires with grout-air-steel interfaces and subjected to various moisture and chloride conditions. By using these models for wires and the experimental data on strands, two probabilistic models are then developed to predict the CT of stressed strands based on the CT of unstressed wires. The developed models can be used to determine the CT of strands with grout-air-steel interfaces subjected to various exposure conditions, provided the CT of corresponding wires under those conditions is estimated. 2014 American Society of Civil Engineers.
