Title: Evaluation of predictions of strand stress at flexural strength for beams with unbonded or combined strands
Date Published: November - December 2026
Volume: 71
Issue: 6
Page Numbers: 72 - 92
Authors: Mi Jin Jung, Pinar Okumus, and Robert J. Frosch
https://doi.org/10.15554/pcij71.6-04
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Abstract
This paper evaluates procedures from design specifications and the literature for predicting strand stress at the nominal flexural capacity of prestressed concrete beams with combined (bonded and unbonded) strands and with only unbonded strands. Flexure test data were compiled for 39 beams with combined strands and 296 beams with only unbonded strands. For beams with only unbonded strands, design specifications procedures based on a bond reduction coefficient, collapse mechanism, or empirical approaches had similar accuracies and predicted the unbonded strand stress well. While conservative, assuming the unbonded strand stress is equal to the effective prestress resulted in inaccurate predictions. For beams with combined strands, predictions were the most accurate when unbonded strand stresses were predicted using the American Association of State Highway and Transportation Officials’ AASHTO LRFD Bridge Design Specifications 10th edition expression meant for beams with only unbonded strands and when bonded strand stresses were predicted using the AASHTO LRFD specifications 10th edition expression meant for members with only bonded strands.