Construction system and construction method of vertical long bundle non-bonded prestressed steel rod for rigid frame bridge

Abstract

The present application relates to the technical field of bridge steel bar construction, and particularly relates to a rigid-frame bridge vertical long-bundle unbonded prestressed steel bar construction system and a construction method. The rigid-frame bridge vertical long-bundle unbonded prestressed steel bar construction system comprises a steel bar group, a positioning suspension frame, an anchoring box and a tensioning assembly. The steel bar group comprises a steel bar and anchorage units arranged at both ends of the steel bar. The positioning suspension frame comprises a fixed frame body and suspension positioning units arranged on the fixed frame body. The suspension positioning units are used for suspending the steel bar group. The anchoring box is arranged corresponding to the steel bar group to form a tensioning groove after pouring. The tensioning assembly is arranged corresponding to the tensioning groove and is used for tensioning the steel bar. The rigid-frame bridge vertical long-bundle unbonded prestressed steel bar construction system and the construction method effectively solve the problems of vertical long-bundle unbonded prestressed steel bar, such as vertical bending, breakage, scratch and the like, by using a suspension type fixed frame body, a fixed plate, a suspension plate and an adjusting screw for supporting and adjusting, and improve the construction efficiency and quality.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of bridge steel bar construction, in particular to a vertical long bundle non-bonding prestressed steel bar construction system and method for rigid frame bridge. BACKGROUND

[0002] In recent years, the highway bridge industry in China has developed rapidly. In the long-span prestressed concrete continuous rigid frame bridge, the finished bridge is often provided with insufficient or missing vertical prestress by using the finished deformed steel bar as the vertical prestress tendon, which causes the problems of beam deflection and web cracking. As a new type of prestressed material, the non-bonding prestressed steel bar has the advantages of high strength, low relaxation, high toughness, high elongation, etc. By applying the special protective lubricating oil for prestress between the steel bar and the sheath and wrapping the outer side of the steel bar with the high-density polyethylene resin sheath, the non-bonding system is formed. The problems of poor relaxation of the traditional finished deformed steel bar, large tendon retraction, inconsistency between the tension force and the theoretical elongation, easy corrosion of the prestress tendon, and slurry leakage during vibration are solved. The corrosion resistance of the prestress tendon is improved. The processes of pre-buried pipe, bundle penetration, and grouting are omitted. The process flow is simplified. The work efficiency is improved. And the loss of vertical stress of the bridge can be effectively controlled.

[0003] However, in the continuous rigid frame bridge with pier beam consolidation, the non-bonding prestressed steel bar as the vertical prestress tendon of the bridge needs to be arranged in a long bundle. The steel bar is pre-buried during the construction of the pier column and is tensioned after the construction is completed. The length of the steel bar can reach 8 to 15 meters. However, due to the small diameter of the non-bonding prestressed steel bar, which is generally only 16 mm, and the large mass and poor stiffness of the long bundle steel bar, the construction hoisting precision is high. During the pre-buried installation of the steel bar in the pier column concrete pouring, the steel bar is prone to vertical bending, damage, scratching, and other problems that affect the prestress. SUMMARY

[0004] In view of this, the purpose of the present application is to provide a vertical long bundle non-bonding prestressed steel bar construction system and method for rigid frame bridge to solve the technical problem that the vertical long bundle non-bonding prestressed steel bar is prone to vertical bending, damage, scratching, and other problems that affect the construction quality in the prior art.

[0005] To achieve the above-mentioned purpose, the technical solution adopted by the present application is as follows:

[0006] The vertical long bundle non-bonding prestressed steel bar construction system for rigid frame bridge comprises:

[0007] The steel bar group is provided in multiple groups and comprises steel bars and anchor unit arranged at both ends of the steel bars. The steel bars are arranged at equal intervals in three. The bottom end of the steel bar is a fixed end, and the top end of the steel bar is a tension end. The fixed end and the tension end of each steel bar are provided with threads. The anchor unit comprises, in sequence from the end of the steel bar away from the end of the steel bar, a spiral tendon, an anchor pad, an anchor nut, an anchor baffle, and an anchor prepared nut.

[0008] A positioning suspension frame includes a fixed frame and at least one set of suspension positioning units mounted on the fixed frame. The fixed frame includes four uprights arranged in a rectangle and a crossbar between two adjacent uprights. The bottom ends of the uprights are embedded in the cast-in-place piers, and the length of the portion of the upright above the pier is greater than the length of the steel bar. The suspension positioning unit is used to position at least two sets of steel bar groups and includes a fixed plate, a suspension plate, and adjusting screws. The fixed plate extends along the direction of the crossbar and is located at the top of the fixed frame. The suspension plate is located below the fixed plate, corresponding to the fixed plate. Adjusting screws are passed through the ends of the fixed plate and the suspension plate. At least two sets of slots are provided along the length direction on the portion of the suspension plate between two adjusting screws. Each set of slots has three slots corresponding to the steel bars in the steel bar group. The slots are used to suspend the steel bar group.

[0009] Anchor box, corresponding to the anchor plate, is set on top of the anchor plate. The bottom of the anchor box is provided with perforations corresponding to the steel bar. The anchor box is used to form a tension groove above the anchor plate when pouring concrete.

[0010] The tensioning assembly includes a tensioning stirrup, an extension rod, a connecting sleeve, a locking wrench, a jack, a tensioning anchor plate, and a tensioning lock nut. The tensioning stirrup is positioned corresponding to the steel bar in the tensioning groove, with a slot at the top for the extension rod to pass through. The tensioning stirrup has holes on all four sides, and the extension rod passes vertically through the slot in the tensioning stirrup. The connecting sleeve is coaxially positioned between the steel bar and the extension rod, with both ends of the adjusting sleeve threadedly connected to the tensioning end of the steel bar and the bottom end of the extension rod, respectively. The locking wrench is mounted on the connecting sleeve and used to tighten the anchor nut on the steel bar. The jack is mounted on the tensioning stirrup for the extension rod to pass through. The tensioning anchor plate passes through the extension rod and is located above the jack. The tensioning nut is threadedly connected to the top end of the extension rod and is used to press against the tensioning anchor plate.

[0011] The beneficial effects of the above technical solution are as follows: The construction system for vertical long-strand unbonded prestressed steel bars of the rigid frame bridge of the present invention is equipped with a positioning suspension frame. After the fixed frame is installed, the steel bar group is suspended by the fixed plate and suspension plate set on the top of the fixed frame, avoiding damage and deformation of the steel bar group due to lack of support during the pouring construction. The construction system for vertical long-strand unbonded prestressed steel bars of the rigid frame bridge of the present invention is continuously improved on the basis of traditional technology. In view of the unique structural form of the new material unbonded prestressed steel bars, a double anchoring combination of high-strength anchor nuts, anchor baffles and anchor spare nuts is used for prestressing anchoring. By using angle steel frame, fixed plate, suspension plate and adjusting screw for support and adjustment, and setting up a suspended fixed frame, a series of problems such as sag, breakage and scratch of vertical long-strand unbonded prestressed steel bars are effectively solved, while improving construction efficiency and achieving significant construction results.

[0012] Furthermore, a strip-shaped screw hole is provided on the fixed plate at the position where the adjusting screw passes through. The strip-shaped screw hole extends along the length of the fixed rod, and the width of the strip-shaped screw hole is adapted to the diameter of the adjusting screw. A circular screw hole is provided on the suspension plate at the position where the adjusting screw passes through.

[0013] Beneficial effect: The position of the steel bar can be precisely adjusted through the screw hole, ensuring the accurate installation position of the steel bar assembly.

[0014] Furthermore, the upright is composed of multiple connecting segments, and a connecting steel plate is fixedly installed at the connection position of any two adjacent segments.

[0015] Beneficial effects: Connecting multiple connecting rod segments reduces the length of a single upright, facilitating processing and transportation, and the connection strength between two adjacent connecting rod segments is improved by setting connecting steel plates.

[0016] Furthermore, a foam board is provided between the anchor box and the anchor plate, and the size of the foam board is the same as that of the anchor plate.

[0017] Beneficial effects: By setting up foam boards to fill the gap between the anchor plate and the anchor box, the seepage of concrete slurry during the pouring process and the surface contamination of the anchor plate caused by later construction are effectively prevented. This reduces the subsequent cleaning work of the tensioning groove and avoids the risk of steel bar retraction and stress loss caused by incomplete cleaning of concrete laitance, fine stones and other debris between the nut and the anchor plate during stress anchoring.

[0018] Furthermore, within the same suspension unit, straight steel bars are installed at equal intervals along the vertical direction, and these straight steel bars are used to connect the various steel bars.

[0019] Beneficial effect: Positioning of steel bars in each suspension unit ensures accurate positioning of the steel bars during concrete pouring.

[0020] The construction method for vertical long-strand unbonded prestressed steel bars in rigid frame bridges includes the following steps:

[0021] S1. Pre-embed positioning suspension frames in the already poured pier section;

[0022] S2. Position and install the prepared steel bar assembly on the positioning suspension frame;

[0023] S3. Concrete is poured in sections for the positioning suspension frame, and anchor boxes for tensioning are pre-embedded during the final concrete pouring.

[0024] S4. Once the concrete reaches the design strength, remove the anchor box and install the tensioning assembly at the tensioning groove formed by the anchor box to vertically tension the steel bar group. After tensioning is completed, lock each steel bar group.

[0025] S5. Pour anchoring concrete into the tensioning trough.

[0026] The beneficial effects of the above technical solution are: the construction method of vertical long unbonded prestressed steel bars for rigid frame bridges of the present invention is simple to operate. By setting up positioning suspension frames, the steel bar groups are supported and fixed, which effectively solves a series of problems such as bending, breakage and scratching of vertical long unbonded prestressed steel bars. At the same time, it improves construction efficiency and achieves significant construction results.

[0027] Furthermore, the positioning suspension frame in S1 includes a fixed frame and at least one set of suspension positioning units installed on the fixed frame. The fixed frame includes four uprights arranged in a rectangular shape and a horizontal bar installed between two adjacent uprights. The bottom end of the upright is embedded in the cast-in-place pier, and the length of the part of the upright above the pier is greater than the length of the steel bar. The suspension positioning unit includes a fixed plate, a suspension plate, and adjusting screws. The fixed plate extends along the direction of the horizontal bar and is installed at the top of the fixed frame. The suspension plate is installed below the fixed plate, corresponding to the fixed plate. Adjusting screws are installed at both ends of the fixed plate and the suspension plate. At least two sets of slots are provided along the length direction on the part of the suspension plate between two adjusting screws. Each set of slots has three slots corresponding to the steel bars in the steel bar group. The slots are used to suspend the steel bar group.

[0028] Beneficial effects: The steel bar assembly is connected to the fixed frame by the suspension plate and the adjusting screw, which not only provides support and fixation for the steel bar assembly, but also allows the height of the steel bar assembly to be adjusted by the adjusting screw, making the hoisting of the steel bar assembly simpler and less labor-intensive.

[0029] Furthermore, a strip-shaped screw hole is provided on the fixed plate at the position where the adjusting screw passes through. The strip-shaped screw hole extends along the length of the fixed rod, and the width of the strip-shaped screw hole is adapted to the diameter of the adjusting screw. A circular screw hole is provided on the suspension plate at the position where the adjusting screw passes through.

[0030] Beneficial effect: The position of the steel bar can be precisely adjusted through the screw hole, ensuring the accurate installation position of the steel bar assembly.

[0031] Furthermore, in S3, a foam board is placed between the anchor box and the anchor plate in the steel bar assembly before the anchor box for pre-embedding tensioning.

[0032] Beneficial effects: By setting up foam boards to fill the gap between the anchor plate and the anchor box, the seepage of concrete slurry during the pouring process and the surface contamination of the anchor plate caused by later construction are effectively prevented. This reduces the subsequent cleaning work of the tensioning groove and avoids the risk of steel bar retraction and stress loss caused by incomplete cleaning of concrete laitance, fine stones and other debris between the nut and the anchor plate during stress anchoring.

[0033] Furthermore, the tensioning assembly in S4 includes a tensioning stirrup, an extension rod, a connecting sleeve, a locking wrench, a jack, a tensioning anchor plate, and a tensioning lock nut. The tensioning stirrup is positioned corresponding to the steel bar in the tensioning groove, with a slot at the top for the extension rod to pass through. The tensioning stirrup has holes on all four sides, and the extension rod passes vertically through the slot in the tensioning stirrup. The connecting sleeve is coaxially positioned between the steel bar and the extension rod, and both ends of the adjusting sleeve are threadedly connected to the tensioning end of the steel bar and the bottom end of the extension rod, respectively. The locking wrench is mounted on the connecting sleeve and used to tighten the anchor nut on the steel bar. The jack is mounted on the tensioning stirrup and is used for the extension rod to pass through. The tensioning anchor plate passes through the extension rod and is located above the jack. The tensioning nut is threadedly connected to the top end of the extension rod and is used to press against the tensioning anchor plate.

[0034] Beneficial effects: By setting up tensioning stirrups to provide support for the jacks, and the holes on the four end faces of the tensioning stirrups to provide space for the use of locking wrenches, it is convenient to tighten the anchor nuts during the tensioning of the steel bar, thereby improving the tensioning efficiency of the tensioning assembly on the steel bar. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the connection between the steel bar and the fixing frame in the construction system of vertical long-strand unbonded prestressed steel bars for rigid frame bridges of the present invention.

[0036] Figure 2 This is a schematic diagram of the steel bar anchorage in the vertical long-strand unbonded prestressed steel bar construction system for rigid frame bridges of the present invention;

[0037] Figure 3 This is a structural schematic diagram of the column extension position in the vertical long-strand unbonded prestressed steel bar construction system for rigid frame bridges of the present invention.

[0038] Figure 4 This is a schematic diagram of the structure of the fixed plate and the suspension plate in the construction system of vertical long-strand unbonded prestressed steel bars for rigid frame bridges of the present invention;

[0039] Figure 5 This is a schematic diagram of the connection between the anchor box and the anchor plate in the construction system of vertical long-strand unbonded prestressed steel bars for rigid frame bridges of the present invention.

[0040] Figure 6 This is a schematic diagram of the tensioning component in the construction system of vertical long-strand unbonded prestressed steel bars for rigid frame bridges according to the present invention.

[0041] Explanation of reference numerals in the attached drawings: 1-Steel bar, 2-Helical reinforcement, 3-Anchor plate, 4-Anchor nut, 5-Anchor baffle, 6-Anchor nut, 7-Fixed frame, 8-Upright pole, 9-Connecting steel plate, 10-Fixing plate, 11-Suspension plate, 12-Strip bolt hole, 13-Circular bolt hole, 14-Slot, 15-Adjusting bolt, 16-Adjusting nut, 17-Locking nut, 18-Straight steel bar, 19-Anchor box, 20-Lifting ring, 21-Tensioning groove, 22-Foam board, 23-Tensioning stirrup, 24-Extension rod, 25-Connecting sleeve, 26-Locking wrench, 27-Jack, 28-Tensioning anchor plate, 29-Tensioning lock nut, 30-Pier column. Detailed Implementation

[0042] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0043] A specific embodiment of the construction system for vertical long-strand unbonded prestressed steel bars of the present invention for rigid frame bridges is as follows:

[0044] like Figures 1 to 6 As shown, the vertical long-strand unbonded prestressed steel bar construction system for long-span continuous rigid frame bridges of the present invention includes steel bar groups, positioning suspension frames, anchor boxes 19, and tensioning components.

[0045] like Figure 1 and Figure 2 As shown, the steel bar assembly consists of multiple groups, including steel bars 1 and anchor units located at both ends of the steel bars 1. Three steel bars 1 are evenly spaced. The bottom end of each steel bar 1 is the fixed end, and the top end is the tensioning end. Both the fixed and tensioning ends of each steel bar 1 are threaded. The anchor unit includes a spiral reinforcement 2, an anchor plate 3, an anchor nut 4, an anchor baffle 4, and an anchor spare nut 6, arranged sequentially at the corresponding ends of the steel bars 1 in a direction away from the end of the steel bar 1.

[0046] like Figure 1 , Figure 3 and Figure 4As shown, the positioning suspension frame includes a fixed frame body 7 and two sets of suspension positioning units mounted on the fixed frame body 7. The fixed frame body 7 includes four uprights 8 arranged in a rectangular shape and a crossbar positioned between two adjacent uprights 8. The bottom end of the uprights 8 is embedded in the cast-in-place pier column 30, and the length of the portion of the upright 8 above the pier column 30 is greater than the length of the steel bar 1. In this embodiment, the uprights 8 are composed of multiple connecting segments. A connecting steel plate 9 is fixedly installed at the connection position of any two adjacent segments. The connection of multiple connecting segments reduces the length of a single upright 8, facilitating processing and transportation. The connection strength between two adjacent connecting segments is improved by the installation of the connecting steel plate 9. The suspension positioning unit includes a fixed plate 10, a suspension plate 11, and an adjusting screw 15. The fixed plate 10 extends along the direction of the crossbar and is located at the top of the fixed frame body 7. The suspension plate 11 is positioned below the fixed plate 10, and the two ends of the fixed plate 10 and the suspension plate 11 are respectively provided with adjusting screws 15. A strip-shaped screw hole 12 is provided on the fixed plate 10 at the position where the adjusting screw 15 passes through. The strip-shaped screw hole 12 extends along the length direction of the fixed rod, and the width of the strip-shaped screw hole 12 is adapted to the diameter of the adjusting screw 15. A circular screw hole 13 is provided on the suspension plate 11 at the position where the adjusting screw 15 passes through. Two sets of slots 14 are provided along the length direction on the portion of the suspension plate 11 between the two circular screw holes 13. Each set of slots 14 has three slots corresponding to the steel rods 1 in the steel rod group, and the slots 14 are used to suspend the steel rod group.

[0047] like Figure 5 As shown, the anchor box 19 is positioned on top of the anchor plate 3, corresponding to the anchor plate 3. The bottom of the anchor box 19 has perforations corresponding to the steel rod 1. A pair of lifting rings 20 are installed on one of the inner sidewalls of the anchor box 19. The anchor box 19 is used to form a tension groove 21 above the anchor plate 3 during concrete pouring. A foam board 22 is placed between the anchor box 19 and the anchor plate 3. The size of the foam board 22 is the same as that of the anchor plate 3. The foam board 22 fills the gap between the anchor plate 3 and the anchor box 19, effectively preventing the infiltration of concrete slurry during pouring and preventing surface contamination of the anchor plate 3 during later construction. This reduces the subsequent cleaning work of the tension groove 21 and avoids the risk of stress loss due to incomplete cleaning of concrete laitance, fine stones, and other debris between the nut and the anchor plate 3, which could cause the steel rod 1 to retract.

[0048] like Figure 6As shown, the tensioning assembly includes a tensioning stirrup 23, an extension rod 24, a connecting sleeve 25, a locking wrench 26, a jack 27, a tensioning anchor plate 28, and a tensioning lock nut 29. The tensioning stirrup is positioned corresponding to the steel rod 1 in the tensioning groove 21, with a slot at the top for the extension rod 24 to pass through, and holes on all four sides. The extension rod 24 passes vertically through the slot in the tensioning stirrup. The connecting sleeve 25 is coaxially positioned between the steel rod 1 and the extension rod 24. Both ends of the adjusting sleeve are threadedly connected to the tensioning end of the steel rod 1 and the bottom end of the extension rod 24, respectively. The locking wrench 26 is fitted onto the connecting sleeve 25 and used to tighten the anchor nut 4 on the steel rod 1. The jack 27 is mounted on the tensioning stirrup 23 for the extension rod 24 to pass through. The tensioning anchor plate 28 is inserted through the extension rod 24 and located above the jack 27. The tensioning nut is threaded to the top of the extension rod 24 and is used to press it onto the tensioning anchor plate 28.

[0049] The specific working principle of the vertical long-strand unbonded prestressed steel bar construction system for rigid frame bridges of the present invention is as follows: a positioning suspension frame is pre-embedded in 30 sections of the already poured pier column. The prepared steel bar group is positioned and installed on the suspension plate 11 through the slot 14. The length of the adjusting screw 15 between the fixed plate 10 and the suspension plate 11 is adjusted by turning the adjusting nut 16 to adjust the elevation of the steel bar 1. The position of the suspension plate 11 is finely adjusted by moving the entire suspension plate 11 through the strip screw groove 12. After the position of the steel bar 1 is determined, the positioning suspension frame is poured with concrete in sections. When the last section of concrete is poured, the tensioning anchor box 19 is pre-embedded. After the concrete reaches the design strength, the anchor box 19 is taken out, and the tensioning component is installed at the tensioning groove 21 formed by the anchor box 19 to perform vertical tensioning of the steel bar 1. During tensioning, the steel bar group is locked by the anchoring nut 4. After tensioning is completed, the anchoring baffle 5 and the anchoring nut 6 are installed, and the sealing concrete is poured in the tensioning groove 21.

[0050] The construction system for vertical long-strand unbonded prestressed steel bars in rigid frame bridges of this invention is a continuous improvement on traditional processes. Addressing the unique structural form of the new material, unbonded prestressed steel bars, it employs a dual anchoring combination of high-strength anchor nuts, anchor baffles, and anchor spare nuts for prestressed anchoring. By utilizing angle steel frames, fixing plates, suspension plates, and adjusting screws for support and adjustment, and setting up a suspended fixing frame, it effectively solves a series of problems such as sagging, breakage, and scratches that easily occur in vertical long-strand unbonded prestressed steel bars. Simultaneously, it improves construction efficiency and achieves significant construction results.

[0051] A specific embodiment of the construction method for vertical long-strand unbonded prestressed steel bars of the present invention for rigid frame bridges is as follows:

[0052] It should be noted that the construction method of vertical long-beam unbonded prestressed steel bars for rigid frame bridges of the present invention is based on the construction system of vertical long-beam unbonded prestressed steel bars for rigid frame bridges described in the above embodiments, and specifically includes the following steps:

[0053] S1. Pre-embed positioning suspension frames in the already poured pier section;

[0054] S2. Position and install the prepared steel bar assembly on the positioning suspension frame;

[0055] S3. Concrete is poured in sections for the positioning suspension frame, and anchor boxes for tensioning are pre-embedded during the final concrete pouring.

[0056] S4. Once the concrete reaches the design strength, remove the anchor box and install the tensioning assembly at the tensioning groove formed by the anchor box to vertically tension the steel bar group. After tensioning is completed, lock each steel bar group.

[0057] S5. Pour anchoring concrete into the tensioning trough.

[0058] In S2, the steel bar assembly is constructed as follows:

[0059] ① Calculate the length of each vertical prestressing tendon and the total number of steel bars according to the design drawings, as the basis for material cutting.

[0060] ② Based on the length of the steel bar, calculate the theoretical elongation of a single steel bar and determine the thread processing length of the fixed end and tensioning end of the steel bar to ensure that the steel bar threads have sufficient length for stress anchoring. The theoretical elongation (mm) of unbonded prestressed steel bars can be calculated according to the following formula in the "Technical Specification for Unbonded Prestressed Concrete Structures" (JGJ 92-2016):

[0061]

[0062] In the formula: F pm —The average tension force (N) of the unbonded prestressed tendons;

[0063] L p —Length of unbonded prestressed tendons (mm);

[0064] A p —Cross-sectional area of ​​unbonded prestressed tendons (mm2);

[0065] E p — Modulus of elasticity of unbonded prestressed tendons (N / mm2).

[0066] ③ Based on the calculated cutting parameters, unbonded prestressed steel bars are fabricated by a professional manufacturer, and the fabrication is strictly carried out in accordance with the standard "Steel Bars for Prestressed Concrete". After the steel bars are fabricated, the unbonded prestressed steel bars and anchorages are tested for mechanical properties by a qualified testing and inspection unit, and a relevant report is issued.

[0067] ④ Unbonded prestressed steel bars use threaded anchors, allowing for pre-assembly of the anchors before the overall installation of the prestressing tendons. The following describes the assembly method and requirements for steel bars, using a group of 3 φ16 bars as an example from this project.

[0068] 1) According to the design requirements, classify and group the steel bars of the same location and length to be installed.

[0069] 2) Assemble the anchorages at the fixed end and tensioning end in the following order: spiral reinforcement (φ0.8mm) + anchor plate (17mm thick connecting steel plate) + anchor nut (M17*1.5-25mm thick high-strength nut) + anchor baffle (8mm thick connecting steel plate) + anchor spare nut (M17*1.5-17mm thick high-strength nut).

[0070] Assembly of fixed-end anchors: First, install the spiral reinforcement, then insert the anchor plate through the ends of the three steel bars simultaneously, then tighten the anchor nut, push the anchor baffle to fit tightly with the anchor nut, and finally tighten the anchor nut to ensure that the outer steel bar of the anchor nut has a 10mm exposed thread length.

[0071] Tensioning end anchor assembly: The assembly method is basically the same as that of fixed end anchor. First, the spiral reinforcement is installed, then the anchor plate is installed and the anchor nut is screwed in. The thread length of the nut is controlled to be about 6cm. The anchor baffle and anchor nut are not installed first, but are installed and anchored after tensioning.

[0072] The fabrication methods for the positioning suspension brackets and the installation methods for the long steel bar assemblies in S1 and S3 are as follows:

[0073] ① Before the concrete pouring of the pier column above the pre-embedded steel bar section, 5*5cm equilateral angle steel uprights are pre-embedded at 2m intervals around the top of the pier. The pre-embedding can be done by welding with the pier column reinforcement. The pre-embedding depth is not less than 30cm and the exposed length is not less than 1.5m. The pre-embedding should ensure that the members are vertical and the deviation is not greater than 5mm.

[0074] ② After the pre-embedded parts are completed, the segmental concrete is poured. During the pouring, the vibration of the pre-embedded parts should be strengthened to ensure that the concrete around the pre-embedded parts is fully vibrated and compacted.

[0075] ③ Before binding the reinforcing bars in the pre-embedded section, weld and extend the angle steel uprights, and calculate the upright length in advance to ensure that the top elevation of the upright is 10-15cm higher than the design elevation of the steel bar. Angle steel extensions can be achieved by attaching a 5mm connecting steel plate for welding, with a weld length of no less than 30cm. After the uprights are extended, use φ20mm ordinary steel bars as horizontal bars, connecting them horizontally and vertically at 1.5m intervals to form a fixed frame. Use a level and steel ruler to measure and mark the design elevation of the steel bar on the uprights.

[0076] ④ After the fixed frame is installed, the fixing plates and suspension plates on the fixed frame are processed. The fixing plates and suspension plates are made of 5*5cm equilateral angle steel, and the processing length is 5cm longer than the horizontal spacing of the fixed frame. The fixing plate has a 20*50mm strip screw hole at each end, and the suspension plate has a 40*18mm groove in the middle according to the position of the steel bar, and a φ20mm screw hole at each end.

[0077] ⑤ Measure and mark out the position of the steel bars according to the design. Accurately weld the fixing plate to the crossbar of the fixed frame according to the marked position. Then, install an M18 adjusting nut at the top of each screw hole on the fixing plate. Insert a φ18mm, 20cm long screw through the adjusting nut and the fixing plate, and correspondingly insert a suspension plate. The suspension plate should be positioned 10cm below the fixing plate, and secured at the bottom with two M18 nuts. Next, use the tensioning end nut of the steel bar to insert the assembled steel bar into the slot of the suspension plate, forming the steel bar suspension positioning. Fine-tune the position of the steel bar through the strip screw holes on the fixing plate, and precisely adjust the vertical elevation of the steel bar by rotating the adjusting screw.

[0078] ⑥ After the elevation of the steel bar is accurately adjusted, the position of the anchor plate at the fixed end is corrected again, and φ16mm straight steel bars are installed layer by layer along the steel bar every 2m to tie and position it with the steel bar, so as to achieve the effect of precise positioning of long bundle unbonded prestressed steel bars.

[0079] In S3, the method for segmented casting of the positioning suspension frame and installation of the anchor box is as follows:

[0080] After the concealed works have passed inspection, concrete is poured in layers. Before pouring, geotextile is used to fill the tensioning groove anchor boxes to prevent concrete from flowing in during the pouring process. The pouring is carried out synchronously and symmetrically in strict accordance with the design requirements, using φ30 and φ50mm immersion vibrators. During the vibration process, the fixed end of the steel bar and the anchorage of the tensioning end should be appropriately strengthened, but it is strictly forbidden to touch the steel bar and anchorage to prevent displacement or damage. The vibration continues until the concrete achieves good compaction and the surface is flat and covered with slurry.

[0081] After the concrete is poured, cover it with geotextile and water it for curing. The curing time shall not be less than 7 days. Once the concrete has reached a certain strength, remove the anchor box in time and cut the φ16mm rubber tube into 6cm sections, which are then fitted onto the threaded ends of the steel bars for protection. During high-temperature construction in summer, cover the concrete with a film and geotextile, and install sprinkler pipes for continuous water spraying curing. During winter construction, cover the concrete with a film, quilts, and rainproof tarpaulins, and take measures such as lighting a stove or setting up a small heater inside the chamber to raise the temperature of the inner chamber and achieve the desired curing effect.

[0082] During the final concrete pour, anchor boxes were made on the top of the pier using 5mm connecting steel plates, according to the designed tensioning groove dimensions. Steel rod holes were drilled on the bottom of the anchor boxes according to the designed positions, and φ16mm steel bar lifting rings were welded on both sides of the anchor boxes to facilitate subsequent demolding and removal.

[0083] When installing the 5mm thick polyethylene foam tensioning groove anchor box, first loosen the anchor nuts at the tensioning end, and then insert a foam board of the same size and shape as the anchor plate along the steel bar, ensuring that the foam board is in close contact with the surface of the anchor plate. Next, align the holes of the anchor box with the steel bar and insert it, then tighten the anchor nuts to form a seamless combination of anchor plate + polyethylene foam board + anchor box.

[0084] By installing polyethylene foam boards to fill the gap between the anchor plate and the tensioning groove anchor box, the seepage of concrete slurry during the pouring process and the surface contamination of the anchor plate caused by subsequent construction are effectively prevented. This reduces the subsequent cleaning work of the tensioning groove and avoids the risk of steel bar retraction and stress loss during stress anchoring due to incomplete cleaning of concrete laitance, fine stones and other debris between the nut and the anchor plate.

[0085] In S4, the construction method for tensioning and locking the steel bars is as follows:

[0086] Tensioning platform installation: After the concrete age and strength meet the design requirements, clean the tensioning groove, and use a through-hole jack for tensioning. A fixed steel stirrup is installed at the top of the jack, and the vertical prestressed steel bars and through-hole extension rods are tightened together using tensioning connecting sleeves. The specific method is as follows:

[0087] ① Tighten the anchor nuts and anchor plates according to the same requirements to ensure tight contact.

[0088] ② Use a 2cm connecting steel plate to make a steel trestle as a tensioning platform. The top of the trestle should have a slot for the extension rod to facilitate the insertion of the extension rod. The trestle should have holes on all four sides to facilitate the anchoring of the nuts.

[0089] ③ Insert the nut anchoring and locking wrench, and then align the top slot of the steel trestle tensioning platform with the position of the steel bar. The installation of the tensioning platform must ensure that the four legs of the trestle are reliably and stably supported on the concrete surface.

[0090] ④ Install a through-hole jack on the tensioning platform. Align the center of the jack with the center of the steel bar through the slot of the tensioning platform. Then, tighten the tensioning connecting sleeve to the steel bar and the extension rod in the same way.

[0091] ⑤ Insert the tensioning anchor plate into the top of the extension rod and tighten the tension lock nut until all tensioning equipment and components are installed.

[0092] Vertical steel bar tensioning: 1. Vertical unbonded prestressed steel bars are tensioned single-end by single branch. The concrete strength before tensioning should meet the design requirements (reach 90% of the design strength). 2. Tensioning must be carried out symmetrically and synchronously on both sides of the web. For vertical unbonded prestressed steel bars on the same web, the middle tendon is tensioned first, followed by the two side tendons. 3. Tensioning is controlled by both tension force and elongation, with tension force as the primary control and elongation as the verification. The difference between the actual elongation and the theoretical elongation should be controlled within 6%.

[0093] The tensioning procedure shall be performed in accordance with the following provisions:

[0094] 0→0.1→1.00 (Simultaneously tighten the anchor nut) → Hold the load for 2 seconds and then lock the anchor nut.

[0095] ① Before tensioning the steel bar, first read the initial elongation value 'a' on the jack scale and record it;

[0096] ② Start the oil pump and apply tension stress. When the oil gauge reading reaches the pressure value corresponding to 10% of the tension control force, immediately turn off the oil pump, read the elongation value b, and record it.

[0097] ③ Start the oil pump and continue to apply stress. At the same time, rotate the locking handle to lock the anchor nut synchronously. When the oil gauge reading reaches the pressure value corresponding to 100% of the tension control force, immediately turn off the oil pump, read the elongation value c, and make the corresponding record.

[0098] ④ After holding the load for 2 seconds, use the locking handle to tighten the anchor nut.

[0099] The actual elongation ΔL is calculated based on the measured elongation value. ΔL = cba. The difference between the actual elongation and the theoretical elongation should be controlled within ±6%. If it is not within this range, tensioning should be stopped immediately, the cause analyzed, and tensioning resumed only after the problem is resolved. After all steel bars are tensioned, anchor baffles and anchor nuts are installed promptly to form a double anchoring system.

[0100] In S5, the construction method for pouring anchor sealing concrete into the tensioning channel is as follows:

[0101] After tensioning and anchoring, the tensioning end should be sealed and protected as soon as possible to prevent the anchor plate and steel bar from being exposed for a long time, causing pollution and corrosion. The sealing should use concrete of the same strength as the box girder. Before sealing, use an air compressor to blow away debris from the tensioning groove, moisten it with water, and then pour the concrete. After the concrete is compacted by vibrating rods and the concrete is sealed and anchored, the concrete is smoothed around the edges with a wooden trowel and covered with plastic film for water retention and curing.

[0102] The construction method of vertical long-strand unbonded prestressed steel bars for rigid frame bridges of the present invention is simple to operate. By setting up positioning suspension frames, the steel bar groups are supported and fixed, which effectively solves a series of problems such as drooping, breakage and scratching of vertical long-strand unbonded prestressed steel bars. At the same time, it improves construction efficiency and achieves significant construction results.

[0103] The embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A construction system for vertical long-strand unbonded prestressed steel bars for rigid frame bridges, characterized in that, include: The steel bar assembly consists of multiple sets, including steel bars and anchor units set at both ends of the steel bars. Three steel bars are set at equal intervals. The bottom end of the steel bar is the fixed end and the top end of the steel bar is the tensioning end. Each steel bar has threads at both the fixed end and the tensioning end. The anchor unit includes a spiral bar, an anchor plate, an anchor nut, an anchor baffle, and an anchor spare nut arranged sequentially at the corresponding ends of the steel bars in the direction away from the ends of the steel bars. A positioning suspension frame includes a fixed frame and at least one set of suspension positioning units mounted on the fixed frame. The fixed frame includes four uprights arranged in a rectangle and a crossbar between two adjacent uprights. The bottom ends of the uprights are embedded in the cast-in-place piers, and the length of the portion of the upright above the pier is greater than the length of the steel bar. The suspension positioning unit is used to position at least two sets of steel bar groups and includes a fixed plate, a suspension plate, and adjusting screws. The fixed plate extends along the direction of the crossbar and is located at the top of the fixed frame. The suspension plate is located below the fixed plate, corresponding to the fixed plate. Adjusting screws are passed through the ends of the fixed plate and the suspension plate. At least two sets of slots are provided along the length direction on the portion of the suspension plate between two adjusting screws. Each set of slots has three slots corresponding to the steel bars in the steel bar group. The slots are used to suspend the steel bar group. Anchor box, corresponding to the anchor plate, is set on top of the anchor plate. The bottom of the anchor box is provided with perforations corresponding to the steel bar. The anchor box is used to form a tension groove above the anchor plate when pouring concrete. The tensioning assembly includes a tensioning stirrup, an extension rod, a connecting sleeve, a locking wrench, a jack, a tensioning anchor plate, and a tensioning lock nut. The tensioning stirrup is positioned corresponding to the steel bar in the tensioning groove, with a slot at the top for the extension rod to pass through. The tensioning stirrup has holes on all four sides, and the extension rod passes vertically through the slot in the tensioning stirrup. The connecting sleeve is coaxially positioned between the steel bar and the extension rod, with both ends of the adjusting sleeve threadedly connected to the tensioning end of the steel bar and the bottom end of the extension rod, respectively. The locking wrench is mounted on the connecting sleeve and used to tighten the anchor nut on the steel bar. The jack is mounted on the tensioning stirrup for the extension rod to pass through. The tensioning anchor plate passes through the extension rod and is located above the jack. The tensioning nut is threadedly connected to the top end of the extension rod and is used to press against the tensioning anchor plate.

2. The construction system for vertical long-strand unbonded prestressed steel bars of rigid frame bridges according to claim 1, characterized in that: The fixed plate is provided with a strip-shaped screw hole at the position where the adjusting screw passes through. The strip-shaped screw hole extends along the length of the fixed rod, and the width of the strip-shaped screw hole is adapted to the diameter of the adjusting screw. The suspension plate is provided with a circular screw hole at the position where the adjusting screw passes through.

3. The construction system for vertical long-strand unbonded prestressed steel bars of rigid frame bridges according to claim 1, characterized in that: The upright is composed of multiple connecting segments, and a connecting steel plate is fixedly installed at the connection position of any two adjacent segments.

4. The construction system for vertical long-strand unbonded prestressed steel bars for rigid frame bridges according to any one of claims 1-3, characterized in that: A foam board is provided between the anchor box and the anchor plate, and the size of the foam board is the same as that of the anchor plate.

5. The construction system for vertical long-strand unbonded prestressed steel bars for rigid frame bridges according to any one of claims 1-3, characterized in that: Within the same suspension unit, straight steel bars are installed at equal intervals along the vertical direction. These straight steel bars are used to connect the various steel bars.

6. A construction method for vertical long-strand unbonded prestressed steel bars in a rigid frame bridge, characterized in that, Includes the following steps: S1. Pre-embed positioning suspension frames in the already poured pier section; S2. Position and install the prepared steel bar assembly on the positioning suspension frame; S3. Concrete is poured in sections for the positioning suspension frame, and anchor boxes for tensioning are pre-embedded during the final concrete pouring. S4. Once the concrete reaches the design strength, remove the anchor box and install the tensioning assembly at the tensioning groove formed by the anchor box to vertically tension the steel bar group. After tensioning is completed, lock each steel bar group. S5. Pour anchoring concrete into the tensioning trough; The positioning suspension frame in S1 includes a fixed frame and at least one set of suspension positioning units installed on the fixed frame. The fixed frame includes four uprights arranged in a rectangle and a crossbar installed between two adjacent uprights. The bottom end of the upright is embedded in the cast-in-place pier, and the length of the part of the upright above the pier is greater than the length of the steel bar. The suspension positioning unit includes a fixed plate, a suspension plate, and adjusting screws. The fixed plate extends along the direction of the crossbar and is installed at the top of the fixed frame. The suspension plate is installed below the fixed plate, corresponding to the fixed plate. Adjusting screws are installed at both ends of the fixed plate and the suspension plate. At least two sets of slots are provided along the length direction on the part of the suspension plate between two adjusting screws. Each set of slots has three slots corresponding to the steel bars in the steel bar group. The slots are used to suspend the steel bar group.

7. The construction method for vertical long-strand unbonded prestressed steel bars of rigid frame bridges according to claim 6, characterized in that: The fixed plate is provided with a strip-shaped screw hole at the position where the adjusting screw passes through. The strip-shaped screw hole extends along the length of the fixed rod, and the width of the strip-shaped screw hole is adapted to the diameter of the adjusting screw. The suspension plate is provided with a circular screw hole at the position where the adjusting screw passes through.

8. The construction method for vertical long-strand unbonded prestressed steel bars of rigid frame bridges according to claim 6, characterized in that: In S3, a foam board is installed between the anchor box for pre-embedded tensioning and the anchor plate in the steel bar assembly before the anchor box is pre-embedded.

9. The construction method for vertical long-strand unbonded prestressed steel bars of rigid frame bridges according to claim 6, characterized in that: In S4, the tensioning assembly includes a tensioning stirrup, an extension rod, a connecting sleeve, a locking wrench, a jack, a tensioning anchor plate, and a tensioning lock nut. The tensioning stirrup is positioned corresponding to the steel bar in the tensioning groove, with a slot at the top for the extension rod to pass through. The tensioning stirrup has holes on all four sides, and the extension rod passes vertically through the slots in the tensioning stirrup. The connecting sleeve is coaxially positioned between the steel bar and the extension rod, and both ends of the adjusting sleeve are threadedly connected to the tensioning end of the steel bar and the bottom end of the extension rod, respectively. The locking wrench is mounted on the connecting sleeve and is used to tighten the anchor nut on the steel bar. The jack is mounted on the tensioning stirrup and is used for the extension rod to pass through. The tensioning anchor plate passes through the extension rod and is located above the jack. The tensioning nut is threadedly connected to the top end of the extension rod and is used to press against the tensioning anchor plate.

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