Effects of temperature on the delayed behavior of biaxially prestressed concrete
Résumé
The delayed deformations of prestressed concrete structures under sustained loading exhibit a non-linear progression over time, impacting tension in the prestressed tendons and causing a subsequent decline in compression within containment vessel walls of nuclear power plants. Maintaining compression within these walls is critical for ensuring tightness under various operational conditions. Design codes provide analytical formulas for assessing these deformations, primarily based on tests involving prestressed concrete in a single direction, such as bridge decks. However, discrepancies between on-site measurements and analytical formulas arise in the case of biaxially prestressed structures such as containment vessels. Moreover, the impact of temperature on the kinetics of measured delayed deformations is overlooked in Eurocode 2 formulas. This study is a part of the European project ACES (Assessment of safety performance of Civil Engineering Structures), aiming to assess the analytical formulas of fib model code 2020 to address effects like biaxial prestressing, temperature, loading history on the evolution of concrete strains over time. The planned experimental program includes various Thermo-Hydro-Mechanical configurations, enriched by a few additional ones from other ACES project studies. It comprises two types of creep tests, uniaxial and biaxial loading, on small concrete slabs. These samples are instrumented with fiber optic sensors to measure strains in the three directions throughout the test period. The presented results pertain to temperatures of 20°C and 38°C in water conditions and are compared with those from databases of other studies from literature. Comparing experimental measurements with fib model code formulas will guide modifications to account for temperature effects, particularly in bi-axially prestressed structures.