AASHTO LRFD bridge design specifications provisions for loss of prestress

| PCI Journal 108 A new method for estimating time-dependent loss of prestress was introduced in the 2005 interim revisions of the American Association of State Highway and Transportation Officials’ AASHTO LRFD Bridge Design Specifications following the recommendations of the National Cooperative Highway Research Program’s (NCHRP) report 496. The primary goal of the research documented in NCHRP report 496 was to update the methodology for estimating prestress loss, extending its applicability to include high-strength concrete girders. The method that was developed (and has since been adopted as AASHTO LRFD specifications article 5.9.5.4) is much more refined and rigorous than previous AASHTO methods. The refinements, while in many ways making the method more technically sound, introduce some nuances that can be confusing to practitioners more familiar with previous approaches. The goal of this paper is to clarify the AASHTO LRFD specifications loss of prestress provisions by demonstrating their foundation in basic mechanics.