bridge using pc strand

Low relaxation pc strand

ISO 9001:2008, ISO14001:2004 Qualified ;
Low relaxation PC strand application for large-span bridges on railways and highway,rock-soil anchoring project,
multi-story industrial buildings,stadiums,coal mines,domes for nuclear power stations and etc.
Manufacturer comply to standard ASTM A416, BS5896, AS1311, JISG3536, ISO6934, EN10138

Low Relaxation PC Strand

Prestressing construction
Large reinforced concrete beam due to design or construction errors, the material does not match the requirements, the use of functional changes, the temperature difference is too large, suffered disaster damage and durability and other reasons, there will be value exceeding the design specification allows structural cracks, or cause insufficient carrying capacity should be measures taken to reinforce reinforcement processing.
Under the existing reinforcement procedures described in the main reinforcement methods are: increased cross-section reinforcement method, Steel Reinforcement Act, to change the structure of power transmission pathways reinforcement method, member outer bonding steel reinforcement method non-prestressed reinforcement method, and traditions in order to Ⅰ or Ⅱ grade steel as a reinforcing steel rod horizontal rod method, under-supporting rod France and modular trolley law prestressed reinforcement method.
The main advantage of prestressed reinforcement method is quick, with prestress, then crack width smaller arch girders counter-productive. Original steel stress immediately becomes small, is active reinforcement method. For the next-supporting prestressed reinforcement rod method, while also reinforcing positive oblique section section strength and intensity. It also an obvious advantage is available for high reinforcing rib section. Prestressed reinforcement method rather than a passive reinforcement method, the deformation of the beam to be to continue to increase gradually after work, so after the crack width and deflection reinforcement will continue to increase, and is inclined section section strength and general strength can not be strengthened.
However, the traditional method of prestressing reinforcement Thanks to low intensity, poor flexibility, short length of steel grade Ⅰ or Ⅱ as a reinforcing steel rod, there is the following disadvantages:
1 When you need to assume greater force rod, the material is very large so that the construction is very difficult;
2, prestressed value is not high, the proportion of prestressing loss is relatively large, long prestressed ineffective.
3, tie rod ends fixed to be welded, not allowed to have the fire place for inappropriate use.
4, to bent three polygonal and more difficult for horizontal tensile, bending friction at large.
5, can not engage in continuous span reinforcement.
To overcome these shortcomings, the author since 1988, under the traditional method of supporting prestressed reinforcement rod developed on the basis of a high-strength steel strands with glossy as a reinforcing rod "High Strength Wire Prestressing law. " Specific design and construction methods see reference [1], [2]. The law has been reinforced with dozens of projects over 1000 cross-beams, reinforcement achieved satisfactory results. This method uses a glossy reinforced high-strength steel cable, a manual method of transverse tensile prestress. This technology is in the beam prestressing reinforcement works in one application methods. The author in recent years, have developed a kind of high-strength unbonded strand as a reinforcing rod, using jacks longitudinal tension, transverse tension or hand, or a combination of both methods prestressed prestressing reinforcement technology . The following will detail this reinforcement method.
First, the design method
1, strand arrangement
W unbonded specifications generally use φj15 (7φS5), ultimate strength of 1570N/mm2 or 1860N/mm2, arranged in pairs on both sides of the beam, to the beam centroid strand side distance is generally 40mm or so. Strand should be required to make up the shape of the bending moment graph similar. Under normal circumstances, the use of two strands can meet the requirements, the number of strand when you need a lot of reinforcement can be arranged in rows. In order not to affect the use of clear height, you can put strand across the supporting point located above the bottom of the beam position. Strand can be continuous across the layout, in order to enhance the structural integrity and to simplify the node structure.
2, iron settings: In order to form the shape of the design requirements strand to strand the turning point in the set bearing pad or steel hanging sticks and other pieces of iron, steel plate to be set at both ends or steel pin stick.
3, the middle point of the practice of successive book: When using multi-span continuous tensioning strand across the turning point located above the bottom of the beam position, in order to reduce friction at the turning point, in the middle on both sides of the bearing to be set steel hanging rod. If the turning point in a cross-strand located in the beam at the end the following location, not to set the intermediate bearing steel hanging rod, strand linked directly supported on beams or sub-beams on, but it should be set in a cross-tighten the bolts.
4, the end of the anchoring method:
Strand ends of the anchor sleeve three clips using garden-style fixture. End bearing may use the following two methods:
1), when there is a vertical support surface, the jig through the steel plate can be supported on the beam end;
2), can not be set when the steel plate, the available coring machine at the upper end of the beam cross-section drilling, set park steel pin stick, the jig rod bearing steel pins through the park on the end of the beam. When poor quality concrete beams can be set with the Park diameter steel pin steel rod of the same diameter pad, sit with rapid hardening cement mortar slurry.
5, prestressing method:
When using a continuous strand cross the arrangement, but the turning point in the cross located above the bottom of the beam position, should be adopted in order to reduce tension across the longitudinal friction losses; when the strand across the turning point in the beam end of the following locations, we can use one end of the longitudinal tension, but later in the longitudinal tension, should also be used in cross-tighten the bolts in the lateral tension to cover the friction caused by the loss of prestress values. When there are difficulties longitudinal tension can also be a turning point in the beam across the bottom, all with transverse tension approach. This method is generally applicable to the non-appearance of the requirements of the situation.
Longitudinal tensioning tool uses feedthrough jacks and high-pressure pumps, hydraulic tensile force directly from the table to read. Transverse tension tighten by hand tightening bolts U-shaped nut, so that the side of the beam to the beam bottom strand rope intermediate position * so strand elongation to cover pre-stressed. Transverse tension can use handheld extensometer readings strand elongation, and thus obtain prestress values.
6, the tensile stress control values: When using the jack longitudinal tension, the strand tensile stress control value is generally desirable 0.7fptk, when continuous span across a few more, we can use 0.75fptk. When all the sheets by hand horizontal pull when tensile stress control values ​​should be appropriately reduced, in order to avoid excessive plastic deformation, stress affect test accuracy, and generally 0.6fptk so. Fptk strand tensile strength for the standard value.
7, anti-corrosion measures: When using unbonded as a reinforcing rod, generally belonging to the ceiling of the situation required, or without considering the appearance of the requirements of the situation. Iron and steel wire can be used C30 fine aggregate concrete or cement mortar 1:2 respectively parcels.
Second, the member strength calculation method to determine the number required to pass strand strength calculation
Since strands bonded together with no concrete girders, each strand cross-section section of other parts of the strain and the strain does not meet the plane section assumption, so up strand stress increment limit state calculations become quite complex, in addition to the use of the cross section of the axial force balance and moment balance two static equilibrium conditions, but also by the following deformation compatibility conditions: two anchor end strand between the total value of elongation and strand fiber cross-section with a height equal to the total value of elongation. According strand usually takes the shape and form of interaction and cross-sectional load stiffness curve, using the integral method. Taking into account the limited number of the reinforcing member and the amount strand reinforcement costs throughout the proportion is not large, so a conservative approximation can be calculated. Calculation, you can assume up to limit state prestressing strand stress is when tension control stress, assuming that the stress increment value strand prestressing loss values ​​are equal. So they can be as ordinary as reinforced concrete beam sections and oblique sections for positive strength calculation.
For ultra-rib section, can be caused by prestressing equivalent load to balance out the part of the external load, and then reducing the strength calculation of the cross-section masterpiece. Then you can consider only the original cross-section reinforcement.
If the original cross-section not super tendons section, in considering the role of prestressing strand tendons later became a super-sectional, it should be calculated with the method described above to compare the calculated results, whichever is the greater value.
Third, unbonded prestressing reinforcement method has the advantage with smooth transverse tensioning strand prestressing reinforcement method, as with the traditional method of prestressing reinforcement comparison has the following advantages:
1, due to strand high strength to withstand greater force when necessary rod, the material does not need a large area, the construction is more convenient.
2, due to tensile stress is high, the proportion of prestressing loss is small, so long prestressing effect.
3, the end of the anchor can be used with existing fixtures, safe and reliable, without on-site fire welding, wide application.
4, strand flexible, very easy to form the shape of the design, construction a lot easier.
5, due to the length of the strand length, can be used across a continuous reinforcement, strengthening the structural integrity.
6, the construction speed, and not subject to temperature effects.
7, girders reinforced clear height has little effect on housing.
8, since the intensity of the original beam can be fully utilized, but only need to reinforce the beam itself, pillars and foundation could not addressed, so reinforcing relatively low cost.
Unbonded prestressing reinforcement method with smooth strand prestressing reinforcement method, also has the following advantages;
1, due to unbonded in less friction at the turning point, you can use the jack longitudinal tension, thus reducing the workload of tension, and tension values ​​easily controlled.
2, due to unbonded corrosion resistance is better, less demanding in the case of the appearance, corrosion can take simple measures, the construction more convenient.
3, strand storage convenience, will not rust.
4, with less iron

 

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