Proposed lump-sum formulas for long-term prestress losses

[摘要] The approximate formula for estimating long-termprestress losses in the ninth edition of the AmericanAssociation of State Highway and TransportationOfficials’ AASHTO LRFD Bridge Design Specifications1is the outcome of the research work presented in NationalCooperative Highway Research Program (NCHRP) report496 Prestress Losses in Pretensioned High-Strength ConcreteBridge Girders.2 The approximate formula was derived bysimplifying the detailed method and taking into account thevariability of concrete properties and the interaction betweenprecast concrete girders and a cast-in-place concrete deck.Two detailed parametric studies are presented in this paperbased on the average conditions for the design and construction of commonly used bridge girders. The girders examined were two bulb tees (BT-54 and BT-72), three I-girders(NU1100, NU1600, and NU2000), two box beams (BI-48and BIII-48), one inverted tee (IT600), and one slab beam(SIV-48). Three spans and, consequently, three levels ofprestressing for each section were considered. The first studyestablished the creep multiplier Nc, while the second studyevaluated the shrinkage multiplier Ns. Both multipliers areused in lump-sum formulas for estimating long-term prestresslosses for different bridge girders. The multipliers derivedfrom these studies were compared with that of the AASHTOLRFD specifications approximate method, and new lump-sumformulas for long-term prestress losses are proposed.

[学科分类] 建筑学