Proposed criteria to determine experimentally the transmission length of prestressed reinforcement

Abstract

[EN] In pretensioned concrete, the force in the prestressing reinforcement is transferred to the concrete by bond in the end region of the member. The distance from the end of the member over which the effective prestressing force is developed is called transmission length. Two indirect methods to determine the transmission length have been habitually used: measurement of the strain in the surface of the concrete and measurement of the reinforcement end slip.

Groups of specimens with different embedment length with the objective to experimentally determine the transmission length had been tested. The ECADA method based on the analysis of the supported force by the strand in different sections of a prestressed concrete element have been applied. The specimens had also been instrument with lineal slips measurement devices, in each end of the specimen. The bond phenomena are not disturbed by any of the measurements devices.

The ECADA method criteria to determine the transmission length had been applied. The force vs. strand end slips relations during the release had been analyzed. A sequence of slips values in each end of the specimen after the release, in correspondence to the embedment length tested had been obtained.

The sequence of slips values (at both ends of the specimen) show a bilinear behaviour, a falling branch with increasing embedment lengths and a horizontal branch, this, corresponding to the cases of embedment length equal or higher to the transmission length. Therefore, both strand end slips sequences allow to establish new criteria to experimentally determine the transmission length.

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