Post-tensioned segmental concrete bridges are often used for long, multispan viaducts or medium-span valley and river crossings. This article presents the research that led to the development of the equation for predicting stresses in unbonded tendons at ultimate; this equation is currently used in the AASHTO LRFD Specifications and AASHTO Guide Specifications for the Design and Construction of Segmental Concrete Bridges. The research, performed by the late Robert J. G. MacGregor, involved the construction and testing of a 1/4 scale model of a three-span, continuous, precast segmental-concrete box girder bridge, erected using span-by-span techniques and post-tensioned with external tendons. The authors discuss the results of the tests to ultimate that were dominated by flexural behavior. Predicted tendon stress increases are then compared to a large data base from other tests of beams and slabs with unbonded tendons. The authors conclude that the equation proposed by MacGregor predicts the tendon stress increases in unbonded tendons conservatively and relatively well, compared to expressions that ignore tendon length.


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  • Accession Number: 00987527
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Mar 17 2005 12:00AM