Prestress Losses in Pretensioned Girders Part II: Experimental Program

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Title: Prestress Losses in Pretensioned Girders Part II: Experimental Program

Author(s): N. Al-Omaishi and M.K. Tadros

Publication: Special Publication

Volume: 228

Issue:

Appears on pages(s): 461-480

Keywords: creep; high-strength concrete; long-term materialproperties; modulus of elasticity; prestress loss; prestressedconcrete; relaxation; time-dependent materials properties

Date: 6/1/2005

Abstract:
Prestress loss estimation is required for properly assessing concrete stresses and member deformation. Earlier methods of prestress loss prediction were based on relatively low concrete strength. Their use for high strength concrete can produce significant errors due to their inability to accommodate varying material properties. Another source of error for earlier methods is that they do not adequately address the interaction between precast concrete members and cast-in-place composite topping. This paper presents the results of the research work conducted by Tadros et al.1 in the National Cooperative Highway Research Program (NCHRP) 18-07 study on prestress losses in high strength concrete which have been adopted by the American Association of State Highway and Transportation Officials, Load and Resistance Factor Design, AASHTO LRFD Specifications2 for inclusion in the 2005 Edition. This is the second part of a two parts paper. Part I described the development of the new methods that were applicable to conventional and high strength concrete ranging from 4 to 15 ksi (28 to 103 MPa). This Part II deals with the experimental program of prestress losses in seven full-scale bridge girders. These girders are in four different states; Nebraska, New Hampshire, Texas and Washington that represent four different regions. Previously reported measurements of thirty-one pretensioned girders in seven different states are also examined.