Currently there is an extensive variety of tendons available for prestressed concrete with widely varying bond properties. An investigation was carried out into the bond development length characteristics of a 9.3mm indented prestressing strand. The primary objective was to determine whether this strand would be suitable for use in prestressed concrete railway sleepers.
Railway sleepers require maximum tensile strength at the rail seats but there is limited space for development of the tendon strength, so the requirements of the bond between the concrete and the tendon in this area are particularly severe. Past research has shown that current Australian code provisions for the required development length are quite conservative. Refinement of the code requirements would lead to a reduction in materials and cost and, therefore, more economic sleeper design.
An experimental study was carried out which consisted of direct pullout tests in which the fully stressed strand was encased in concrete and tested for pullout failure. The concrete was prestressed and steam cured in the usual manner for railway sleepers. From these test results, it was concluded that the code requirements for the development length were conservative.
An analysis was carried out to attempt to determine a local bond stress versus slip relationship which could predict the test results obtained. The bond stress-slip model used was of the type given in the European code for traditional concrete reinforcement. This analysis was duplicated for the pullout test results obtained from a previous experimental study on a 5mm indented prestressing wire. By altering the parameters given in the European code, an excellent prediction of the experimental results was achieved. This determined appropriate bond stress-slip relationships for the 9.3mm strand and 5mm wire which could be used for future investigations of bond characteristics.