Construction Technology of Low Retraction Anchorage
(1) Pre-cast of components of channels and under anchorages
- Factors such as the length of the structural channel, the dead-end length, the thickness of the bearing plate at the stressing end, the length of the tensioning jack, and the tensioning process should be considered when calculating the cutting length of the steel strand.
- A grinding machine is used for steel strand cutting, and arc cutting shall not be used.
- The extruding anchor is produced by a barrel swager. After extrusion, insert the steel strand and the extruding anchor into the dead-end bearing plate according to the requirements of the drawing, and press the extruding anchor on the bearing plate with the pressure cover, bolts, and nuts.
- Braid and bundle the steel strands.
- Insert the steel strand bundle into the restraining ring and corrugated duct. Insert one end of the grouting pipe into the corrugated ducts from the restraining ring, and seal the ducts with tape at the restraining ring.
- Set up a fixed support point at a distance of 0.8-1.5m to fix the corrugated duct on the non-prestressed tendons to ensure that the corrugated duct is not positioned and moved when pouring concrete.
- Install the stressing-end bearing plate.
- Seal the connection between the bearing plate and the corrugated duct with tape to prevent the mortar from infiltrating into the channel.
(2) Concrete pouring
- Before concrete pouring, check whether the installation of steel strands, prestressed anchorages, and corrugated ducts meets the requirements.
- Concrete pouring shall be implemented in accordance with Article 12.7 of JTJ041-2000 Technical Specification for Construction of Highway Bridges and Culverts.
- When pouring concrete, special attention should be paid not to vibrating the ducts, bearing plates, and other precast components to prevent leakage and dislocation.
- Prestressed equipment (tensioning jacks, electric oil pumps, etc.) shall be implemented in accordance with Articles 12.8.1 and 12.8.2 of JTJ041-2000 Technical Specifications for Construction of Highway Bridges and Culverts.
- The control stress of the first tension should be over-tensioned by 5% according to the design tension control stress, and the control stress of the second tension should meet the design requirements. In any case, the tension control stress should not be greater than 0.8fpk.
- The steel strand is tensioned by the stress control method and checked by the elongation value.
- The components should be inspected before tensioning. The concrete strength of the components shall meet the design requirements. When the design is not determined, it should not be lower than 90% of the design strength.
- The first tension can be done with a mono-strand jack. When the number of steel strands is more than 3 (including 3) or the length of the steel strand is greater than 8 meters, the group tension should be carried out. The second tension should use group tension.
(4) Channel grouting
The channel grouting shall be carried out in accordance with Article 12.11 of JTJ041-2000 Technical Specifications for Construction of Highway Bridges and Culverts.