Assessment of Thermal Prestress Loss with Re-Tensioning Tests

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Title: Assessment of Thermal Prestress Loss with Re-Tensioning Tests

Author(s): Songhee Lee, Yeonhee Kim, Minhyeok Ko, and Chadon Lee

Publication: Structural Journal

Volume: 116

Issue: 6

Appears on pages(s): 87-96

Keywords: analysis; pretensioning; re-tensioning test; steam curing; test; thermal prestress loss

Date: 11/1/2019

Abstract:
Re-tensioning tests were performed and analyzed to measure the thermal prestress loss (ΔfT) caused by elevated temperatures during the curing of precast and prestressed concrete members. A total of eight prismatic concrete beams were pretensioned with strands 12.7 mm (0.5 in.) in diameter. Experimental parameters were the concrete strength (f ′cd), initial prestress (fpi), and curing condition (steam curing versus air-dry curing at ambient temperature). Analytical expressions were derived for changes in prestress at different curing stages. Using those expressions and the retensioning test results, the time and temperature at bonding between the strand and the surrounding concrete were identified. The results indicate that ΔfT was only marginally influenced by f ′cd and fpi. However, ΔfT was observed to increase almost linearly with the additional increase in temperature until bonding.