Equivalent Strain Distribution Factor for Unbonded Tendon Stress at Ultimate

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Title: Equivalent Strain Distribution Factor for Unbonded Tendon Stress at Ultimate

Author(s): Keun-Hyeok Yang and Thomas H.-K. Kang

Publication: Structural Journal

Volume: 108

Issue: 2

Appears on pages(s): 217-226

Keywords: equivalent strain distribution factor; post-tensioned beam; stress; unbonded tendon

Date: 3/1/2011

Abstract:
A simple approach is proposed to predict the stress at ultimate and the corresponding incremental stress in unbonded tendons of simply supported post-tensioned beams. To evaluate the total elongation of the unbonded tendon between two anchorages, an equivalent strain distribution factor is established from the distribution of concrete strains at the tendon level along the beam length. The concrete strain distribution is calculated using the nonlinear two-dimensional (2-D) analysis, which is based on the methodology proposed by Naaman and Alkhairi. The effects of the loading type and tendon profile on the tendon stress increase of a beam are considered in the proposed equivalent strain distribution factor. Data from a total of 209 simply supported beams are compiled and compared with those determined from prior empirical and code equations. Whereas the accuracy of existing models depends on the loading type, the proposed model generally gives better agreement with the test data, is not sensitive to the loading type, and is marginally dependent on the span-depth ratio.