Issued as a Documentation Report on The Field Investigation of Prestressed Reinforced Concrete Highway Bridges, Project IHR 93, Phase 1, Illinois Cooperative Highway Research Program

摘要

Theoretical time-dependent deformations and prestress losses in pretensioned,prestressed simply supported concrete girders, based on the revised rate of creepmethod, are presented. The effects of age of precast girders at the time ofcasting of the deck concrete, time of transfer of prestress, deck dead load,type of prestressing strands (stress-relieved or low-relaxation strands), initiallevel of stress in the concrete, and the effects of varying environmental conditionson the behavior of concrete structures are studied.Predicted unit creep and shrinkage strains versus time relationships arebased on the 1970 C.E.B. recommendations and relaxation losses for stress-relievedstrands are estimated using the expressions developed by Magura, Sozen,and Siess. A similar expression is used for the case of low-relaxation strands.Predicted deformations are compared with long-term measurements made onfull-sized bridge structures located in Illinois. Annual cyclic variations ofthe total strains and total prestress force occur in all structures locatedoutdoors.Two recommended sets of factors for the estimation of prestress lossesare given, one for the case of stress-relieved strands and the other for thecase of low-relaxation strands.