Unbonded tendons
1 range
This process standard applies to post-tensioned unbonded prestressed concrete structures with 8 degree seismic fortification in Beijing.
2 construction preparation
2.1 Materials and main equipment
2.1.1 The production of non-adhesive steel bars and steel wire should be in line with national standards "prestressed concrete steel wire" (GB5223
A 85), "prestressed concrete strand" (GB5224-85) requirements.
2.1.2 The coating layer of unbonded tendons adopts "special construction grease". Its performance and product quality index shall conform to the standard issued by Hunan Bureau of Standards on June 6, 1983. On July 1, 1983, the "unbonded prestressed Tendons lubrication with anti-rust grease technical conditions "requirements.
2.1.3 Unbonded tendon cladding material is made of low-density high-pressure polyethylene (the melt index is 1.5 ~ 5 at 190 ℃).
2.1.4 The quality requirements of finished unbonded bars shall conform to the requirements of the design and construction regulations for the design and construction of the unbonded prestressed concrete structural system (BUPC) in Beijing (Trial) (DBJ01-7-90) Section 2.2.5 (see Table 4-44). Non-adhesive tendons with steel wire, strand, do not allow a dead bend, see the dead bend must be cut off. Wire should be long, no joints.
2.1.5 The structure and technical requirements of Type A and Type B anchorage systems for unbonded prestressed concrete structures shall comply with the requirements set out in Chapter 3 of Part II of DBJ01-7-90.
The construction of Type A and Type B anchoring systems is shown in Figures 4-52 to 4-57.
The performance and conditions of Type A and Type B anchors are shown in Table 4-45.
Usually with a beam or armor B, stranded with B type.
2.1.6 supporting tensioning equipment with oil pump and jack, the technical performance, see Table 4-46. Machine with the top pressure (hydraulic and spring two), tension rods, tool anchors.
2.2 Operating conditions
2.2.1 When the tensile strength of concrete to meet the design requirements, generally not less than 70% of the design strength, a test report card.
2.2.2 Preparation of unbonded bars and completion of reinforcement processing.
2.2.3 Anchorage has been checked and accepted.
2.2.4 tensioning equipment has been tested, equipment is ready.
2.2.5 Tensioning of the scaffold and fence erection has been completed and checked to meet operational requirements.
2.2.6 According to the requirements of the design of the non-adhesive tendons of the tensioning sequence, tension values, elongation, laying of non-adhesive tendons as well as the operation, quality standards, technical description.
3 operating process
3.1 Process flow:
Construction preparation → beam, plate formwork support → non - prestressed steel laying, banding →
Unbonded prestressed tendon laying, installation of the end node → non-prestressed reinforcement laying, banding →
Unbonded prestressed arching, banding → hidden inspection → concrete pouring and vibrating →
Concrete curing → tension → end treatment
3.2 Check the repair of non-adhesive tendons: non-adhesive ribs approach, it is timely verification of the size of the ribs, size and quantity, the root-check the outer tendon and the quality of the end of the accessories, with A-beam, should Carefully check the inside and outside the anchor cup thread, head upset size, leakage of upsetting phenomenon, etc., and positioning screw into the anchor cup, screw into the depth of Table 4-47. After inspection and correct, can be classified stacking. The wrapped layer of damaged non-adhesive tendons, with plastic tape repair.
3.3 Position of the end hole of the end mold: In the tensioning side of the die, according to the construction drawing, the location of the bond wire, number and drilling. With an anchor bar diameter of φ40, with a bolt hole diameter φ30.
3.4 Installation of bearing plate: The tension plate is installed on the tension-free end of the unbonded tendons, so the tensioning cylinder and the bearing plate are not perpendicular to each other due to the inclination of the bearing plate. The vertical deviation of bearing plate is shown in Section 4.3.
3.5 laying non-adhesive tendons: usually non-adhesive ribs configured with one-way and two-way curve configuration two. Laying should pay attention to:
3.5.1 The unbonded tendons shall be placed at the same horizontal position (cross-center and support) as the non-prestressed tendons in the same direction in order to ensure the high vector requirements of the unbonded tendons.
3.5.2 Before laying, should be iron stool to control the curvature of non-adhesive tendons, generally every 2m set a stool, the height of the stool according to design requirements. Across the middle may not set horse stool, tied directly to the bottom of the bar.
3.5.3 Bidirectional curve configuration, should also pay attention to the placement of tendons. Due to the various points of the ribs are highly different ups and downs, there will be two-way reinforcement staggered phase pressure. In order to avoid laying wear tendons, the construction must be artificial or computer programming. The alignment method is to mark the elevation (from the bottom of the plate to the height of the unbonded tendon epithelium) at the cross point of the unidirectional tendons, and compare the corresponding two elevations of the crossings. If one direction A tendon of the points were lower than the intersection of the corresponding points of the corresponding elevation, then the tendons can be placed first. According to this law to find out the order of laying. In this order, the non-prestressed tendons tendons tied at the end, the non-adhesive tendons laid in the template.
3.5.4 The unbonded tendons shall be laid underneath the ducts to avoid unbonded tendons from pulling downward, resulting in the bending of the ducts and the breakage of the concrete below them.
3.6 End node installation:
3.6.1 A-type anchoring system Tension-side installation: The plastic protective sleeve gently into the reserved hole in the bearing plate to prevent the pouring of concrete, the cement slurry into the anchor cup thread, and affect the tension. According to design requirements, to determine the embedded depth of anchor cup. To ensure the correct position, can be achieved through the positioning link. The length of the connecting rod is 160mm, and the two ends are threaded. One end of the connecting rod is screwed into the anchor cup (the length of which is specified in Table 4-47), the wire is fixed in the end mold on. The depth of the anchor cup is checked by measuring the dimensions of the rod exposed to the end die. In the positioning process, the embedded depth of the anchor cup to be done by root check, check, strictly control the exposed size of the positioning link. Refer to Table 4-47 for the allowable deviation of the exposed dimension of the connecting rod, and the exposed dimension should be calculated according to Figure 4-58.
Lr = A - B -? L + 30 - C
Where Lr - a link exposed in the end of the mold size (mm);
A - connecting rod length;
B- the length of a connecting rod screwed into the anchor cup:
ΔL - Calculate the elongation value (mm) after unbonded tendons are stretched;
C-thickness of the end of the template (mm).
3.6.2 Installation of fixed anchorage system anchorage system: Anchor anchored seven-hole anchor plate is tied to non-prestressed tendons or additional bars with lead wires, and the spiral bars are arranged in the front area to strengthen the concrete Compressive strength. Steel upsetting head should be tight with the anchor plate, flush, does not allow a scattered phenomenon.
3.6.3 Installation of tensioning end of B-type anchoring system: When installing, the unbonded tendons shall be pierced from the reserved hole of the bearing plate, and the vertical section of the bearing plate shall be fastened with lead wire. See Table 4-47 for the length of the inner straight section. When the anchor is recessed into the tensioned end of the concrete, the surface of the plastic plug is coated with oil to prevent adhesion to the concrete. At the same time in the pouring of concrete, the pressure plate to be inside the surface of the location of the prestressed tendons outside the plastic pipe cut along the surrounding, and then removed when the tension.
3.6.4 B type anchoring system anchorage end installation: according to design requirements fixed in the template, and configure the spiral bar. Stranded fixed end needs to be distributed, the seven-hole steel wire head upsetting.
3.7 Lashing: check the plastic protective sleeve without damage. The two ends of the soft plastic pipe are tied to the protective sleeve and non-adhesive tendons, respectively, according to the design requirements will be non-bonded tendons tied to the non-prestressed tendons tendons tendons or additional tendons on the board, lashing should be protected without bonding The tendons coincide with the axes of the anchor cups and are perpendicular to the bearing plates to facilitate the pulling out of the plate end when tensioning.
3.8 arching: tie non-prestressed tendons, according to the construction drawings in the design of the number of non-adhesive tendon position, straighten the bond-free tendon, the alignment curve of the height of the control point below the stool position tied. See Table 4-47 for the quality requirements of tendons for tendons.
3.9 Concrete pouring and vibrating:
3.9.1 After the laying of the unbonded bar assembly is completed, the construction unit, the quality inspection department and the design unit shall jointly carry out hidden inspection and acceptance. When the qualification is confirmed, the concrete shall be poured.
3.9.2 When pouring concrete, do not press the stool and to prevent the touch of a trace to ensure that the non-adhesive tendons and anchors of the location of accurate.
3.9.3 Tension end and anchorage end concrete should be carefully vibrated, forbidden to leak vibration, to avoid honeycomb pock, to ensure its compactness, and is strictly prohibited to touch the tension side of the plastic sleeve, to avoid damage due to sleeve off the impact of Zhang Pull to proceed.
3.10 A-type anchoring process:
3.10.1 Construction preparation: remove the positioning link before the tension, the end of the template, clean-up site, scaffolding support and protective barrier.
3.10.2 Equipment Installation: Screw the tension rod into the anchor cup, install the jack and tighten the tension rod nut (must be full buckle). The jack should be installed on the same axis as the unbonded tendon and perpendicular to the bearing plate. If less than required, can be used pad pad on the end of the support frame to adjust.
3.10.3 Tensioning: Turn on the oil pump and apply pressure. When the pressure gauge reaches 5MPa, stop the pressure, adjust the cylinder position, continue to pressurize until the required tension value, turn off the pump power, stop the oil pressure. And then anchor the buckle outside the buckle clear brush, screw on the nut, once again connected to the pump, pull tension to pull the value, tighten the nut.
The use of electric pump pressure, to control the oil speed, oil pressure to control the general time to the oil can not be less than 0.5min.
Tension process, when the individual wire fracture, the tension can be reduced accordingly. However, the number of breaks should not exceed 2% of the total number of prestressing tendons in the same section. For multi-span biaxially continuous plates, the same section is calculated per span.
3.10.4 Measurement record: In order to check the prestress value, in the process of tension, the elongation value of the unbonded bar should be recorded at random. Usually each level to take the oil pressure gauge readings to multiples of 10MPa is appropriate.
At the beginning of tensioning, the unbonded tendons are free to be placed in the plastic sleeve, which is tightened with a certain tensile force, so that it is difficult to measure the starting point of the tension, the zero point of the unbonded tensile stress One point in theory is the measure of the elongation of the tendons.
The zero point is determined by pressing the jack to 10 MPa, marking the jack as the starting point for measuring the unbonded elongation value, see point A in Figure 4-59, and increasing the pressure gradually to 20 MPa until The final pressure value is reached and the elongation value of each bar is recorded in groups. The B, C, D points in Figure 4-59 can be drawn. Because in the elastic range, the elongation value is proportional to the stress, so the points in Figure 4-59 made a straight line and extended, and the horizontal axis at O1 point, the O1 point is the zero point, The total elongation value should be ΔL1 + ΔL2.
When the measured elongation value and the calculated elongation difference of 10% or more, should be analyzed.
Measured elongation greater than the calculated elongation of 10% or more, should stop the tension, check the meter is wrong, if necessary, should be re-check and calibration.
The measured elongation is less than the calculated elongation value of 10% or more, you should find out the reasons can continue to pressure or non-adhesive bundle to relax, the second tension, but the tensile stress can not exceed the standard non-adhesive reinforcement Pull strength of 75%.
3.10.5 Anchorage and demolition equipment: tighten the nut, you can gradually return to oil, relax the non-adhesive tendons, remove the jack. Operation should be back to the oil slowly, first cut off the power supply, after the valve to move back to the oil position, and then return the oil to the original piston, remove the jack.
Anchorage cup position error caused by tensile force to meet the design requirements, the cup exposed plate face is too long (more than 50mm) or too short (less than 20mm), should be taken to add nuts or anchor bolts for anchoring.
3.11 B-type anchoring process:
3.11.1 Construction preparation: the end of the plate should be cleaned before stripping, stripped of exposed steel wire (steel beam) of the outsourcing of plastic casing, one by one to check the anchor, is strictly prohibited to use a corrosion anchor. And the length of the exposed unbonded ribs was measured one by one, and recorded as the original length before stretching.
3.11.2 tension: connected to the pump, pressure, when the pressure reaches 2.5MPa, stop the pressure. Adjust the position of the jack, continue to pressurize until the tension required to achieve the design. When the dry jack stroke can not meet the required tension elongation value, the way to stop the tension, for temporary anchorage, back jack trip, and then the second tension. Both ends of the tension at the same time, both ends of the tension to maintain the same, the pressure difference should not exceed 10MPa.
3.11.3 Top Pressure and Demolition Equipment: There are two methods of top pressure, hydraulic top pressure and spring top pressure. Hydraulic top pressure is pressurized with a manual pump to the top press. When the tension to control stress, stop the pressure, to maintain the required pressure, with a manual pump to the top of the pressurized, the pressure reaches 30MPa, the top pressure and jack slowly return oil, and finally remove the tensioning device. When the spring top pressure is applied, when the tension is required to control the stress, the oil can be returned. As a result of the spring top press, the anchoring pressure is larger and the anchorage is larger. The second tension, you must remove the top pressure equipment, put on the support frame, the jack support in the component. Tension must be maintained when the jack and anchor on the same axis, the pressure position should take the design control stress value. The use of open-type gasket, pad in the anchor with the pressure plate at the gap.
3.11.4 Measurement record: After measurement, measure the length of the unbonded bars minus the length measured before tensioning. The difference is the actual elongation value, which is used to check the calculated elongation. The deviation is + 10% Or -5%.
3.12 The protection of the anchorage zone shall be adequately protected against rust and fire, and shall be protected against entry of water vapor, corrosion of anchors or prestressing tendons.
There are usually two approaches:
3.12.1 Anchoring Outer-wrapped reinforced concrete ring beams. For A-type anchors, oil guns should be filled with oil-lubricated anti-rust grease into the plastic protective sleeve through the oil-filling hole of the anchor cup, and then filled with oil (grease out from another oil-filled hole) before outsourcing the reinforced concrete . For B-type anchors, the exposed unbonded tendons should be cut off, leaving only 20cm, and then the dispersion of bending, and then pouring concrete.
3.12.2 pre-embedded in the concrete anchorage components, to be tensioned, cut off the excess non-adhesive tendons (must use the wheel saw, not
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