Title:
Unbonded Tendon Stresses in Post-Tensioned Concrete Walls at Nominal Flexural Strength
Author(s):
Richard S. Henry, Sri Sritharan, and Jason M. Ingham
Publication:
Structural Journal
Volume:
109
Issue:
2
Appears on pages(s):
171-182
Keywords:
finite element method; post-tensioning; precast concrete; shear wall; stress; tendon; unbonded
DOI:
10.14359/51683628
Date:
3/1/2012
Abstract:
The accurate prediction of tendon stresses is a critical step in calculating the nominal flexural strength of unbonded post-tensioned concrete walls. The lateral load behavior of these walls is largely characterized by a single crack developing at the wall base with the unbonded tendons providing the tension needed for flexural moment resistance. Unlike members with bonded reinforcement, stresses in unbonded tendons cannot be found from strain compatibility and instead must be related to the wall lateral deformation. Previously developed equations for predicting tendon stresses in unbonded post-tensioned flexural members, including those in ACI 318-08, have focused on concrete beams and are inappropriate for concrete walls. A finite element model validated with experimental data from the testing of concrete walls was used to demonstrate the inaccuracy of current design provisions and other available equations for predicting tendon stresses. To provide a more accurate prediction of the unbonded tendon stresses in post-tensioned concrete walls that are designed for use in regions with low seismicity, an equation is proposed that is suitable for inclusion in future versions of ACI 318.