Prestress Losses in Pretensioned Girders Part I: Method Development


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Title: Prestress Losses in Pretensioned Girders Part I: Method Development

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

Publication: Special Publication

Volume: 228


Appears on pages(s): 439-460

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

Date: 6/1/2005

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 paper consists of two parts. Part I describes the development of the new methods that are applicable to conventional and high strength concrete ranging from 4 to 15 ksi (28 to 103 MPa). Part II deals with the experimental program and comparison of measured versus estimated prestress losses.