Test of 90-Foot Post-Tensioned Concrete Girder with Unbonded Tendons

A full-scale post-tensioned concrete girder with unbonded tendons was tested to investigate whether, under vertical forces, a full flexural mechanism (with three hinging regions) would form, and what strand stress would be reached in that condition. The specimen was a 0.91 m (3 ft) deep T-beam with a 2.43 m (8 ft) wide flange, spanning over two supports spaced at 18.3 m (60 ft) with two 4.6 m (15 ft) cantilevers and featured a parabolic tendon profile. Transverse reinforcement to resist shear and longitudinal "mild" reinforcement were also provided. A uniformly distributed load was applied on the main span and concentrated loads were applied to the ends of the cantilevers. While the main span was loaded, the two concentrated loads on the cantilevers provided a reaction force to minimize rotations at supports. At the end of the test, the girder deflected 278 mm (10.9 in., L/65) and carried 231 kN/m (15.5 kip/ft) over the main span. A full plastic mechanism formed with hinging regions at supports and at midspan. Test results suggest the unbonded tendons nearly reached their nominal strength (f(pu)) and that a limit analysis is adequate for estimating the flexural strength of comparable post-tensioned girders.