Stress at Ultimate in Unbonded Post-Tensioning Tendons: Part 2--Proposed Methodology

Abstract

The first part of this study reviewed existing prediction equations for the stress f sub pm in unbonded tendons at nominal bending resistance, compared prediction equations with experimental results from 143 beam tests reported in the technical literature, and pointed out some of the drawbacks in existing prediction models for f sub ps. In the second part, the background for a new rational methodology for the analysis of beams prestressed with unbonded tendons is covered, and a new prediction equation for f sub ps at ultimate is developed. The equation is shown to account for most of the variables found important in the analysis, and to predict experimental results with much better accuracy than any of the prediction equations reviewed in the first part. The developed equation is proposed for adoption in the ACI Building Code.