Since the adoption of ACI 423.7-14 (Joint ACI-ASCE Committee 423 2014) in ACI 318-14 (ACI Committee 318 2014), the encapsulation of a single-strand PT tendon is required for elevated floors in the United States. Given the condition that PT strands are not bonded to or covered by concrete, the use of encapsulated anchor systems is much needed for the durability of the strand. In this paper, both load-carrying performance and hydrostatic tests of unbonded PT anchors are conducted in accordance with existing specifications or industry/manufacturer standards. The tested encapsulated single-strand anchor was developed by the authors for the first time in Korea, which would provide cost effectiveness and practical feasibility compared to imported anchors. Load-carrying capacity, sustainability, and durability of concrete structures with a variety of materials/products are important considerations and should be meticulously considered (Kang et al. 2009a, 2011, 2014; Yang et al. 2014). The durability design requirements for reinforced and post-tensioned concrete structures are becoming more stringent in the 21st century than a few past decades. The current experimental study is expected to contribute to PT concrete industry in this aspect.
Three specimens (SLT1 ~ 3) were tested. To control both load and displacement, the live-end anchor was set onto a steel frame, which was moved by an actuator, rather than a jacking device (Fig. 2a). LVDT 01 ~ 04 (Fig. 2b) measured the displacement of an anchor plate, core (king) wire, one of the six helical (perimeter) wires, and one set of the wedges. The free length of the strand was 3500 mm. For SLT3, LVDT 05 and LVDT 06 (Fig. 2c) were added to measure the elongation in the middle of the strand, thereby satisfying stipulations in ACI 423.7 (Joint ACI-ASCE Committee 423 2014).
The strand was inserted into the anchor with a wedge, and each anchor was fixed to the steel plates. Both ends were fixed with hinges so that the longitudinal axis was maintained parallel to the ground plane when the strand was elongated. The initial free length of the specimen was 1000 mm. One end was fixed, with repeated loading applied using an actuator at the other end. The repeated loads between 160 and 171 kN were applied at 3 Hz for 2,000,000 cycles.
The partial elongation in the middle of the SLT3 specimen was obtained using the difference between the displacements of LVDT 05 and LVDT 06. The measured portion was much close to the fixed end location. The partial elongation in the middle was very small because the measured original length was only a portion (26%) of the total free length. 2b1af7f3a8