Effect of Member Size and Tendon Layout on Shear Behavior of Post-Tensioned Beams

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Title: Effect of Member Size and Tendon Layout on Shear Behavior of Post-Tensioned Beams

Author(s): Boyan I. Mihaylov, Jian Liu, Konstantine Simionopoulos, Evan C. Bentz, and Michael P. Collins

Publication: Structural Journal

Volume: 116

Issue: 4

Appears on pages(s): 265-274

Keywords: arch action; deformation patterns; kinematic model; shear; size effect; strut-and-tie model

Date: 7/1/2019

Abstract:
Eight post-tensioned beams were tested at the University of Toronto to study the size effect in shear and the influence of different tendon layouts. The specimens varied in depth from 250 to 1000 mm (9.84 to 39.4 in.), while the unbonded tendons were either straight or harped. The eccentricity of the tendons was either zero, 1/6, or 1/2.67 of the section depth. The beams had no stirrups and were tested to shear failure under symmetrical three-point bending. It is shown that the specimens with a shear-span-to-effective-depth ratio of approximately 3 developed arch action and exhibited a size effect. A strut-and-tie model based on the AASHTO code captures the experimental results well, except the high shear resistance observed in the smallest specimens. To explain this behavior and the transition from slender to deep members, the paper sets the basis of a rational modeling approach based on kinematics. It is shown that the complete deformation patterns of the beams, including the width of the shear cracks, can be captured by a kinematic model with only three degrees of freedom.