Prestressed concrete in the construction of some matters that should be paid attention
In the use of prestressed concrete, should pay attention to the following situation, to ensure the safety of both parties.
(1) of the prestressed steel cutting, appropriate USES wheel saws, which arc cutting shall be adopted;
(2) steel wire braided beam, should straighten out by root, tied into a bundle, shall not be disorder.Fixed the steel strand JiYaXing pattern anchorage, anchorage or pressure shall be carried out in advance and bearing plate and spiral reinforcement assembly;
(3) the prestressing with machines and equipment and instrument, should be regular maintenance and calibration;
(4) the former, the prestressed tendon should provide concrete strength testing report.When the compressive strength of concrete meet the design requirements, and not less than 75% of the design strength grade, after adding prestressed;
(5) the former, the prestressed tendon should be clean on board face, and check the bearing plate at the back of the concrete quality.If it has a hollow concrete phenomenon, should be repaired before tensioning with epoxy mortar;
(6) prestressed when installation, the anchor plate is, clamping piece should be matter, and pieces of a uniform: but matter clamp were not overweight, with rabbit jaw knocking bad;
(7), before the formal large-tonnage prestressed tensioning shall, in conjunction with the tensioning professionals to try.Confirm rational tensioning process, a long stretch value is normal, no harmful cracks appear, before tensioning in bulk.When it is necessary to determine the actual channel friction losses.In curve prestressed beam shall not adopt any small jack single tension;In order to avoid unnecessary loss of prestress.When tensioning, the operator must be on the safe side, completes the protective measures, pay attention to the operating personnel is strictly prohibited standing in tension and tensioned prestressed reinforcement when the front;
(8) when tensioning prestressed reinforcement, should start from zero load to measure elongation value at the beginning of the tension, then load classification to the required tension;
(9) prestressed tensioning management, take the stress control, elongation test.The actual elongation value and calculated extension value of allowable deviation of 5% ~ + 10%.If more than the value, tensioning shall be suspended;Measures shall be adjusted, may continue to tension;Such as small elongation, super tensioning measures, but the tension limit shall not be greater than 0.8 FPTK value;In many wave curve prestressed reinforcement, in order to improve the inner support of the tensile stress, reduce after tensioning prestressed tensioning mouth under stress, can adopt super zhang back to pine technology;
(10) dense hole grouting requirements, should not be below the C30 strength grade cement slurry.Before the grouting hole should be moist, clean, grouting should be slow evenly, without interruption, and the exhaust flow.In case of channel blockage, grouting mouth must be replaced, but must be the first pumping slurry discharge, lest two pumping gas exists between the slurry.After filling the hole and closed vent, should continue to pressure to 0.5-0.6 Mpa, closed grouting hole again later.The vertical channel of grouting pressure shall be determined according to the height of grouting;More anchorage content, please visit the universal anchorage net.
(11) with a connector to connect multiple span continuous prestressed duct grouting, should finish pull a across different reperfusion a zhang, not at all across all the tension after a grouting;
(12) exposed after prestressed anchorage length, should not be less than 30 mm, prestressed concrete application of sealing and protection.When need long naked, should take the measures to prevent corrosion;When steel strand has floating rust, please will anchor clamping piece and the outer side steel strand floating rust and dirt removed, when installed and tensioned with the rabbit, free rust, dirt fill clamping piece red tank and cause slippery silk;
(13) tool clamping piece for three panel, job holder for two pills, a mixture of both.Working anchor cannot be used as a tool of anchor can't repeat;
(14) prestressed shall be properly kept, when using, must not have rust, water and other impurities contamination.Work clamping piece to remove the foam can be used inside the box, but when the prestressed beam is longer, must be repeated tensioned anchorage, recommend apply a small amount of lubricant in anchor plate cone hole (e.g., anchor soul back), are not only good for follow-up work clamping piece and back anchor but also to many of the anchorage anchor;Tool clamping piece outer surface and cone hole anchor plate surface coated with lubricant before use, and often remove surface impurities, can make the back anchor flexible, but when the clamping piece crack or tooth surface damage need to change, shall not be used again.
(15) tension when due and security measures, after tensioning jack can't stand people;
(16) anchoring system should be used, can not be used with other system.If you want to do the static load test, please clean with organic solvent (such as gasoline) clamping piece and the anchor plate hole rust-proof oil wipe clean, otherwise will affect anchorage performance;
(17) prestressed construction shall be conducted by professional construction team, and construction personnel should be trained show certificates.