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Behavior of Statically Loaded Pretensioned Concrete Beams with 0.5-Inch Diameter Debonded Strands

Leslie G. Zumbrunnen, Bruce W. Russell, and Ned H. Burns

1992

One of the primary objectives of this research project is to develop design guidelines for the use of debonded, or blanketed, strand. The debonding of pretensioned strand is an alternative to draping strands in order to control the maximum tensile and compressive stresses in pretensioned beams. Debonding strands can simplify girder construction; draping strands is more difficult and more dangerous. Likewise, straight debonded strands enjoy economical advantages to draped strands in the total cost of girders.

Static flexural tests were performed on specimens with debonded strand. An analytical rationale, The Bond Failure Prediction Model, was used to predict cracking and subsequent bond failure for these tests. The agreement between test results and the prediction model was outstanding, demonstrating that a rational design method can be developed for beams with debonded strands. This research also shows that the currently required multiplier of 2.0 for the development length of debonded strand may be significantly reduced, or, more appropriately, the provisions for debonded strand may be changed. Conversely, some dangerous and unsafe designs may be allowed by the current code.

Beams tested in this report were I-shaped and made to resemble an AASHTO section complete with a composite deck. Altogether, ten (10) tests were performed. The beams were loaded statically in flexure until failure. For each test, two types of failure were possible, flexural failure or bond failure. Results from these tests are shown to be accurately predicted by the prediction model.

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