Prestressed Tension Construction Technology Standard

2021-03-19 13:15

1. Scope of use

It is suitable for pre-tensioned pre-tensioned and post-tensioned concrete railways, highways, highway bridges; concrete house construction prefabricated parts factories and on-site prefabrication and construction.

2. Construction Preparation

Preparation of materials and anchors

1) The steel used for prestressed concrete includes: steel wire, steel strand, heat-treated steel, cold-drawn steel, fine-rolled rebar and other pre-stressed steel. The variety, specifications, and diameter must meet the design requirements, and there must be a factory quality certificate and a retest report. The cold-drawn steel bar should also have a test report on the mechanical and technological properties after the cold-drawn.

2) When anchors, fixtures and connectors enter the site, the anchoring performance category, model, specification and quantity should be checked according to the factory certificate or quality certificate, and meet the requirements. The appearance, hardness and static load anchoring performance of anchors and fixtures should be checked before use, and should comply with the current national standard "Anchors, fixtures and connectors for prestressed concrete" (GB/T14370).

Preparation of main equipment

1) Prestressed tension hydraulic jacks, high-pressure oil pumps, external tubing, hydraulic jacks or sand boxes for tensioning, pressure-bearing columns of concrete or steel structures for force transmission, end beams, tool anchors and grouting machines, etc.

2) The machines and instruments used for prestressing should be maintained and checked regularly in accordance with the requirements of the specification. The jack and pressure gauge should be calibrated together.

3. Operating conditions

1) The pre-stressed hydraulic jack, high-pressure oil pump, and stretching machine grouting machine should be checked and recorded. Before use, check whether the tensioning tools and equipment are normal and reliable. If any abnormalities are found, they should be repaired before use.

2) The compressive strength and elastic modulus of the bridge concrete should meet the design requirements; the building construction component concrete must meet the design requirements, if the design does not require it, it should not be less than 75% of the design strength; the geometric dimensions of the bridge and building construction components , Appearance quality, reserved holes and embedded parts should be checked and accepted.

3) The construction site should have approved tensioning procedures and technical measures to ensure product quality and construction safety. The work site should be level and unobstructed to ensure the safety of all construction personnel and equipment.

4) The bridge pedestal should have sufficient strength, rigidity and stability, and meet the needs of construction.

5) The construction personnel who have the knowledge of pre-stress construction and correct operation on site.

6) Anchorages, fixtures and connectors should be prepared and checked and accepted.

7) The pre-stressed tendons or steel stranded wire harness have been made.

8) The mix ratio of the cement paste (or mortar) used for grouting and the mix ratio of the end-capped concrete have been tested and determined.

9) Technical clarification has been carried out, and the tensile tonnage of the prestressed tendons and the corresponding pressure gauge pointer readings, and the calculated elongation value of the steel bars should be written on the row and hung in an obvious position for observation and grasp during operation.