Measuring specific parameters in pretensioned concrete members using a single testing technique

• A testing technique to measure prestressing forces, slips and strains is presented.
• Prestress transfer and loading stages are sequentially performed on a same specimen.
• Series of pretensioned concrete specimens with different embedment lengths are tested.
• Specific parameters in pretensioned concrete members are measured.
• Satisfactory results applicable to the precast concrete industry are obtained.

Pretensioned concrete members are designed and manufactured by using at least two materials: concrete and prestressing reinforcement. Also, two main stages must be considered: prestress transfer and member loading. Hence, the behavior of these members depends strongly on the reinforcement-to-concrete bond performance and prestress losses. In this paper, a testing technique to measure the specific parameters related with the involved phenomena is presented. The testing technique is based on the analysis of series of specimens varying in embedment length to simulate several cross sections at only one end of a pretensioned concrete member. Each specimen is characterized by means of the sequential release of the prestress transfer (detensioning) and the pull-out (loading) operation. The test provides data on prestressing force, transmission length (initial and long-term), anchorage length (without and with slip), reinforcement slips, bond stresses, longitudinal concrete strains, concrete modulus of elasticity, and prestress losses (instantaneous and time-dependent).