Estimated Transfer Lengths of 0.6 in. (15.4 mm) Grade 350 (2400 MPa) Strands in High-Strength Concrete Pretensioned Members

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Title: Estimated Transfer Lengths of 0.6 in. (15.4 mm) Grade 350 (2400 MPa) Strands in High-Strength Concrete Pretensioned Members

Author(s): Jun Ki Lee

Publication: Structural Journal

Volume: 115

Issue: 3

Appears on pages(s): 649-659

Keywords: bonding; high-capacity strand; pretensioned member; transfer length

Date: 5/1/2018

Abstract:
This study investigates the transfer length of 0.6 in. (15.4 mm) Grade 350 (2400 MPa) strand in 11.6 ksi (80 MPa) pretensioned concrete members. The test specimens were fabricated considering an accelerated construction scheme including gradual releasing and strand debonding, along with steam curing to achieve three initial concrete compressive strengths (fci′) of 5.8, 8.7, and 11.6 ksi (40, 60, and 80 MPa). At the release, the longitudinal strain profiles of both strand and concrete were measured using a series of electrical resistance strain gauges (ERSGs) to determine the transfer length. The strain profiles of the strands were in good agreement to those of the concrete and clearly presented the prestress bond transfer from the strand to the concrete. The experimental results indicate that the transfer length of high-strength concrete pretensioned members with Grade 350 strands is well-correlated to the initial compressive strength of concrete (fci′). Also, the transfer length is conservatively predicted using the design provisions in the ACI 318 and AASHTO specifications.