3.4 when pouring concrete, first lay the bottom and vibrate, then penetrate into the steel formwork, and finally pour the second stage concrete.
3.5.3 a p3cm PVC pipe with the same length and thickness of the top plate shall be buried at the mid and quarter points of the hollow slab span to observe the floating and sinking of the air bag.
1.3 on site construction personnel are in place, reasonably configured and complete types of work.
Construction preconditions 1.1 review design documents and conduct technical disclosure.
3.3 the tensioning of prestressed reinforcement shall be carried out according to the design and specifications.
At the same time, pay attention to the embedded reinforcement.
3.1.3 special plastic cushion blocks shall be used for the cushion blocks of reinforcement, the vertical and horizontal spacing shall not be greater than 1m, and the beam bottom shall not be greater than 0.5m..
When the prestressed reinforcement is contaminated with oil, it must be removed.
Construction technology and process 3.1 in order to facilitate demoulding, apply isolation agent to the table and formwork before pouring concrete.
The cutting sequence of prestressed reinforcement on the long line pedestal should start from the tensioning end and cut to the other end step by step.
Construction technology and process 3.1 reinforcement 3.1.1 reinforcement storage, processing and installation shall be carried out in strict accordance with the specifications.
1.2 pedestal, tensioning platform and gantry crane have been completed.
If it is not required by the design, it shall be tensioned in stages, symmetrically and staggered.
Procedure 3.
Sleepers shall be placed horizontally at the end, no stacking is allowed, and the upper arch in the middle of the span shall not exceed 2cm.
4.3 the vibrating rod shall not touch the reinforcement and formwork as much as possible; After the air bag is installed, the lower part of the air bag shall not be vibrated too much to prevent the concrete from squeezing in and floating the air bag.
3.2 the machines, tools, equipment and instruments used for stress application shall be used and managed by special personnel, and shall be maintained and calibrated regularly.
Beams in one contract section shall be prefabricated as much as possible.
It is required to inlay thick and connect tightly.
During reinforcement welding, attention shall be paid to the overlapping length.
If the average retraction value of the steel wire meets the requirements, the tensioning can be formally carried out.
3.5.4 the concrete shall be poured symmetrically and balanced, and the concrete slump shall be about 4cm, which can be summarized in the construction.
Other reinforcement shall be bound on site.
Before tensioning, it is better to cut 2 ~ 3 prestressed steel wires on site and measure the retraction value of the steel wire.
The calibration shall be carried out regularly in the legal measurement technical organization authorized by the competent department.
3.6.5 after all the prestressed tendons are loosened, the exposed reinforcement shall be cut with grinding wheel, and closed with mortar or coated with anti-corrosion materials to prevent rust.
4.
3.5.2 arrange 2 ~ 3 full-length reinforcement on the top of the airbag and connect it with the positioning reinforcement.
Tensioning machines and equipment shall be used together with anchors, and shall be inspected and calibrated when entering the site.
The vibrator shall not collide with the steel strand during laying to prevent accidents.
1.4 mechanical equipment such as Jack, oil pump, reinforcement processing machinery and grouting machine used for precast beam have been mobilized.
1.2 organize the labor force, mechanical equipment and materials required for construction.
01 precast beam construction (pretensioning method) 1.
4.4 when pouring concrete, it shall be carried out in the order of bottom plate, web plate and top plate.
02 precast beam construction (post tensioning method) 1.
Construction quality 4.1 select high-quality concrete, try to use aggregates with large particle size and high strength, and strictly control the concrete slump to reduce the prestress loss caused by concrete shrinkage and creep.
5.
The calibration period of spring dynamometer shall not exceed 2 months.
1.6 tensioning operators must be equipped with walkie talkie to facilitate timely communication and coordination on site.
The axes of the two joint reinforcement shall be consistent.
The reinforcement with a diameter of more than 25 shall be mechanically connected.
The steel wire with more reinforcement shall be tensioned at the same time, and it is not allowed to be tensioned one by one, otherwise the last few steel wires will break suddenly due to excessive tensile force, resulting in cracking at the end of the member.
5.4 protective measures shall be taken when the wire crosses the road.
4.2 an appropriate amount of water reducing agent can be added to the mixture, and the dosage of water, cement and water reducing agent shall be strictly controlled to ± 1% and the dosage of aggregate to ± 2%.
The calibration period during use shall be determined according to the conditions of machines and equipment.
Safety and civilization 5.1 establish a perfect safety responsibility system, which shall be inspected by a specially assigned person.
3.1.2 raw materials and processed reinforcement shall be stacked by category and marked for inspection.
3.6.3 the steel wire with few reinforcement can be sawed and cut one by one.
3.7 the storage period of hollow slab beam shall not exceed 2 months.
2.
3.6.4 for multiple cold drawn reinforcement or steel strand with large tensioning force, it shall be tensioned at the same time.
The jack and the pressure gauge shall be inspected to determine the relationship curve between the tensioning force and the pressure gauge.
5.2 during tensioning, it is strictly prohibited to have miscellaneous personnel near the pedestal, and all construction personnel must wear safety helmets.
1.5 the tensioning equipment has been calibrated by the corresponding qualified department.
3.6.2 the tensioning sequence of prestressed tendons shall meet the design requirements.
The diaphragm reinforcement shall be fabricated in advance and installed as a whole.
The tensioning machines and equipment not used for a long time shall be fully calibrated before use.
3.5 during pouring, the measures to prevent the core formwork of hollow slab from floating, sinking and deviation can be referred to as follows: 3.5.1 bind a P6 positioning stirrup every 1m along the beam length, with the same diameter as the formwork, and connect it with the erection reinforcement of the beam, and bind it firmly.
1.3 the Prefabrication Yard shall be clean, and the layout shall be reasonable and orderly.
When the jack is used for more than 6 months or 200 times, or abnormal phenomena occur during use or after maintenance, it shall be calibrated again.
5.3 safety protection walls with a height of no less than 1.5m shall be built at both ends of the tensioning platform seat to protect the personal safety of tensioning personnel.
2.
7.
Before the prestressed reinforcement is tensioned, the side formwork, flange formwork or inner formwork limiting the displacement shall be removed.
3.6 tensioning of prestressed tendons 3.6.1 during the tensioning of pretensioned prestressed tendons, the strength of component concrete shall meet the requirements of design and specifications.
Procedure (hollow slab as an example) construction preconditions → apply isolation agent → tension steel strand → bind reinforcement → erect side formwork and end formwork → pour concrete → maintenance → seal end concrete → release → move beam 3.
Construction preconditions 1.1 commencement report of subdivisional works and other technical data have been approved and disclosed.
Grade II reinforcement shall adopt knot 502 or knot 506 welding rod.
