This paper presents research conducted under the National Cooperative Highway Research Program (NCHRP) project 18-07, “Prestress Losses in Pretensioned High-Strength Concrete Bridge Girders.�? Thepurpose of this project was to extend the American Association of State and Highway Transportation Officials�? AASHTO LRFD Bridge Design Specifications provisions for estimating prestress losses to cover concrete strengths up to 15 ksi (104 MPa). This paper presents the portion of the work that deals with methods of estimating long-term prestress loss. The results reported in this paper were adopted by AASHTO and included in the 2005 and 2006 interim revisions and in the fourth edition of the LFRD specfications, which was published in 2007. This paper explains the theory of time-dependent analysis. It follows the pseudoelastic, age-adjusted, effective-modulus method. The experimental component consisted of materials properties, which are covered in a companion paper, and prestress loss measurements, which are highlighted in this paper. The measurements were taken in seven girders in bridges in Nebraska, New Hampshire, Texas, and Washington to encompass the regional diversity of environmental and materials properties throughout the country. Theory was also compared with experimental datareported in the literature on 31 pretensioned girders in 7 states.
