Secondary tensioning construction method for prestressed steel strand of lower deck beam of double-deck bridge
By using a steel truss-suspended hanging basket structure for the tensioning platform in a double-deck bridge, the problem of the prestressing tensioning of the lower cap beam being affected by the upper pier columns was solved, achieving safe and stable construction and high-precision prestressing tensioning effect.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- NO 5 ENGINEERING COMPANY LTD OF CCCC FIRST HARBOR ENGINEERING COMPANY LTD
- Filing Date
- 2026-05-18
- Publication Date
- 2026-07-31
AI Technical Summary
In double-deck bridges, the prestressing tensioning of the lower cap beam is affected by the piers of the upper cap beam, making it difficult to move the tensioning platform and achieve reasonable prestressing tensioning.
The tensioning platform, which uses a steel truss hanging basket structure, avoids the upper piers and provides a stable construction space. The accurate positioning and tensioning precision of the steel strands are ensured through the cooperation of corrugated pipes and positioning frames.
This achieved safe and stable tensioning of the lower cap beam, improved construction quality and tensioning accuracy of prestressed tendons, met structural design and durability requirements, and avoided safety hazards.
Smart Images
Figure CN122485170A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of prestressed tensioning construction technology for cap beams, and in particular relates to a method for secondary tensioning of prestressed steel strands in the lower cap beam of a double-layer bridge. Background Technology
[0002] The purpose of tensioning prestressed cap beams is to actively apply compressive stress to the concrete to counteract the tensile stress generated by external loads, thereby reducing the tensile stress of the structure, delaying or even avoiding the occurrence of cracks, and ultimately improving the crack resistance and overall stiffness of the components.
[0003] During the prestressing tensioning construction of the lower cap beam of a double-deck bridge, it was found that if a conventional mobile tensioning platform is used, the presence of piers on the upper cap beam will affect the movement of the tensioning platform. At the same time, how to reasonably tension the prestress of the lower cap beam of a double-deck bridge is also a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention
[0004] In view of this, the present invention aims to propose a method for secondary tensioning of prestressed steel strands in the lower cap beam of a double-deck bridge, so as to tension the prestress of the lower cap beam of the double-deck bridge.
[0005] To achieve the above objectives, the technical solution of the present invention is implemented as follows: The construction method for secondary tensioning of prestressed steel strands in the lower cap beam of a double-deck bridge includes the following steps: S10. Installation of corrugated pipe: A positioning frame is installed along the length of the lower cap beam, avoiding the upper pier column, and the center of the positioning frame coincides with the design center of the lower cap beam duct. Insert the corrugated pipe section by section from one end of the cap beam to the other, and secure the corrugated pipe and the positioning frame firmly. Anchor plates are installed on the end formwork of the cap beam, with the anchor holes of the anchor plates aligned with the ends of the corrugated pipes, and the anchor holes are sealed. S20, steel strand bundle: The cutting length L of the steel strand is equal to the actual length of the duct, the length reserved for tensioning at both ends, and the length clamped by the tool anchor. After the material is cut, use a tool to anchor and comb the bundle, and use an angle grinder to cut off the outer 30-50cm of the steel wire at the end of the steel strand, leaving one steel wire in the middle. Number each steel strand and mark the working anchor in the same way. Fix the remaining steel wire to the traction screw plug, and tie the end with tape. Finally, use a winch to pull the steel strand to complete the bundling. S30, Tensioning Platform Installation: The tensioning platform adopts a steel truss hanging basket structure, and the whole is a counterweight structure. In the area on the top surface of the cap beam that is not covered by the upper structure, the tensioning platform is fixed by truss ballast to keep the tensioning platform in balance. S40. Install the working anchor: Align the working anchor plate with the corresponding holes on the steel strands, ensuring that each steel strand is centered in the hole and does not rub against the hole wall. Then push the working anchor plate inward to make it fit tightly against the flared opening of the anchor plate. S50, pre-tensioning of steel strand: Install a working clamp on one side of the steel strand and an extension sleeve, jack, tool anchor, and tool clamp on the other side. Tension twice at 15% of the control stress under the anchor. S60. Install the jack: Install working clamps at both ends of the steel strand, tighten the clamps with support nuts, and then install tool anchors and jacks on both sides of the steel strand. S70, tensioning: The steel strand is tensioned by jacks on both sides until the prestress test under the anchor is qualified; S80, Finishing: Dismantling the tensioning platform: Grouting is performed from one end of the duct until the other end of the duct is full and the cement grout discharged from the injection hole has the same required fluidity. The grout is continuously sprayed out and the consistency is similar to that of the injected grout. Cut off the exposed steel strands and seal the anchor head with cement grout.
[0006] Furthermore, in step S60, the working anchor, working clamp, tool anchor, jack, and steel strand are concentric.
[0007] Furthermore, in step S70, the tensioning of the prestressed steel strand adopts dual control of tension force and elongation, with the elongation used for verification, and the anchor control stress is 0.70fpk=1302Mpa.
[0008] Furthermore, in step S70, the prestressed steel strand tensioning operation procedure is as follows: 0 → 15%σcon → 30%σcon → 50%σcon → return to 0 for inverted top → 50%σcon → 100%σcon → hold load for 10 minutes → oil cylinder return for anchoring → unload jack.
[0009] Furthermore, in step S80, an abrasive wheel is used to cut the exposed steel strands.
[0010] Furthermore, in step S30, the tensioning platform includes a platform frame, columns, and trusses. The trusses are cantilevered on the cap beam. The platform frame is installed at the outer end of the trusses through the columns. Steel plates are laid inside the platform frame. A counterweight bracket is provided at the inner end of the truss. The counterweight bracket is fixed to the top surface of the cap beam by counterweight blocks.
[0011] Compared with existing technologies, the secondary tensioning construction method for steel strands of the present invention has the following advantages: (1) In this invention, the lower cap beam tensioning platform adopts the structure of the steel truss hanging basket described above. The whole structure is a counterweight structure, which avoids the pier column and provides a safe and stable working space, so that construction personnel can stand on the side of the cap beam at a high position and place the tensioning equipment, avoiding the safety hazards caused by direct suspension or simple hanging basket operation.
[0012] (2) The present invention is used to perform secondary tensioning of the steel strands of the cap beam, ensuring tensioning accuracy and construction quality, and ensuring that the tensioning process of the prestressed tendons is controlled and accurately recorded, thereby meeting the structural design and durability requirements. Attached Figure Description
[0013] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 This is a flowchart illustrating the secondary tensioning construction process of the prestressed steel strands for the cap beam according to an embodiment of the present invention. Figure 2 This is a schematic diagram of the tensioning platform structure in an embodiment of the present invention; Explanation of reference numerals in the attached figures: 1-Platform frame; 2-Column; 3-Truss; 4-Seedling bracket; 5-Counterweight block. Detailed Implementation
[0014] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.
[0015] The construction method for secondary prestressing of the lower cap beam of a double-deck bridge: The second prestressing tensioning of the cap beam needs to be performed after the box girder is erected. The construction process is as follows: Figure 1 As shown, it includes the following steps: S10. Installation of corrugated pipe: A positioning frame is installed along the length of the lower cap beam. The positioning frame is positioned in the steel reinforcement cage, avoiding the upper pier column. The center of the positioning frame coincides with the design center of the lower cap beam duct. Insert the corrugated pipe section by section from one end of the cap beam to the other, and tie the corrugated pipe and positioning frame firmly; after the corrugated pipe is inserted into the steel reinforcement cage, seal both ends with transparent tape to prevent rainwater from entering the corrugated pipe. Anchor plates are installed on the end formwork of the cap beam, with the anchor holes of the anchor plates aligned with the ends of the corrugated pipes, and the anchor holes are sealed. S20, steel strand bundle: Steel strands are inspected in batches, and only those that pass the inspection can be cut. Cutting of steel strands is carried out on a cutting platform to ensure that the steel strands do not touch the ground, and construction is carried out according to regulations. When releasing the steel strands, it is done on a dedicated coiling frame, with cutting starting from the inner end and pulling outwards. The cutting length L of the steel strands is calculated as follows: actual duct length + pre-reserved length for tensioning at both ends + tool anchor clamping length. After the materials are cut, a whole-bundle threading process is adopted. The bundle is combed with a tool anchor, and the outer 30-50cm of the steel wire at the end of the steel strand is cut off with an angle grinder, leaving one steel wire in the middle. Each steel strand is numbered, and the working anchor is also marked to facilitate threading in the order of the numbers when installing the anchor. The reserved steel wire is fixed to the traction plug, and the end is tied with tape. Finally, the steel strand is slowly pulled with a winch to complete the threading. After the steel strand is threaded into the corrugated pipe, the steel strands at both ends are covered with anti-rust sleeves, and the outer layer is sealed with PVC plastic pipe to prevent moisture from entering. S30, Tensioning Platform Installation: The tensioning platform adopts a steel truss hanging basket structure, and the whole is a counterweight structure. In the area on the top surface of the cap beam that is not covered by the upper structure, the tensioning platform is fixed by truss ballast to keep the tensioning platform in balance. The specific structure of the tensioning platform is as follows: Figure 2 As shown, the structure includes a platform frame 1, columns 2, and a truss 3. The platform frame 1 uses [10 channel steel as its skeleton, covered with 3mm checkered steel plates, with a plan dimension of 4.1m × 1.7m. It is surrounded by a 1.2m high guardrail made of 30×30 square steel pipe with a wall thickness of 3mm. The truss chords are made of [8 channel steel, and the web members are made of 50×50 square steel pipe with a wall thickness of 4mm. Four columns 2 are installed, and the platform frame 1 is installed at one end of the truss 3 via these four columns. The construction structure is as follows... Figure 2 As shown, truss 3 is cantilevered on the cap beam, at which time platform frame 1 is in a suspended state; counterweight bracket 4 is set at the inner end of truss 3, and counterweight bracket 4 is fixed to the top surface of cap beam by counterweight block 5. Counterweight block 5 is used as a ballast block, preferably a concrete block, to fix the truss under ballast. S40. Install the working anchor: Align the working anchor plate with the corresponding holes on the steel strands, ensuring that each steel strand is centered in the hole and does not rub against the hole wall. Then push the working anchor plate inward to make it fit tightly against the flared opening of the anchor plate. It should be noted that in this step, all working anchors are installed at the same plane angle; S50, pre-tensioning of steel strand: Install a working clamp on one side of the steel strand, and then install an extension sleeve, jack, tool anchor, and tool clamp on the other side without installing a working clamp. Tension twice at 15% of the control stress under the anchor (once the 15% force value is reached, the jack should immediately return to its original position and not hold the load). S60. Install the jack: Install working clamps at both ends of the steel strand and tighten the clamps with support nuts. Then install tool anchors and jacks on both sides of the steel strand. When installing the jacks and other components, the angle needs to be adjusted to ensure that the working anchor, working clamps, tool anchors, jacks and steel strand are concentric and there should be no gaps or angles. When installing the clamps, use steel pipes to tamp them down and make sure the ends of the clamps are flush. S70, tensioning: The steel strand is tensioned by jacks on both sides until the prestress test under the anchor is qualified, confirming that the prestress under the anchor and the non-uniformity of the same strand meet the requirements. S80, Finishing: Dismantling the tensioning platform: Grouting is performed from one end of the duct until the other end of the duct is full and the cement grout discharged from the injection hole has the same required fluidity. The grout is continuously sprayed out and the consistency is similar to that of the injected grout. Grouting employs an intelligent circulating grouting sequence from bottom to top, with grout entering from the next pipe and circulating to exit from the previous pipe, ensuring continuous circulation of the grout throughout the pipes and expelling air. Grouting is continuous and completed in one go, with a grouting pressure of 0.7 MPa. Grouting should achieve fullness at the other end of the duct, ensuring that the grout discharged from the injection hole has the same fluidity as the required cement grout, with continuous spraying and a consistency similar to the injected grout. After closing the outlet valve, a pressure stabilization period of greater than 0.5 MPa is maintained for 10 minutes. Disposable PVC valves are used and removed only after the grout has solidified. The tensioning groove is promptly sealed with C50 concrete of the same grade as the cap beam. Before pouring the sealing concrete, the anchor surface is roughened, rinsed, and cleaned to facilitate bonding between the old and new concrete. After grouting is completed, long-term rust prevention measures are taken for the reserved steel strands: first, wrap the steel strands with plastic film, then wrap them with geotextile, then cover the steel strands with rust-proof sleeves, and finally seal them with PVC plastic pipes. Use a grinding wheel to cut the exposed steel strands and seal the anchor head with cement grout.
[0016] In a preferred embodiment, in step S70, the tensioning of the prestressed steel strand adopts dual control of tension force and elongation, and the elongation is used for verification. The control stress under the anchor is 0.70fpk=1302Mpa.
[0017] In a preferred embodiment, the prestressed steel strand tensioning operation procedure in step S70 is as follows: 0 → 15%σcon → 30%σcon → 50%σcon → return to 0 for inverted top → 50%σcon → 100%σcon → hold load for 10 minutes → oil cylinder return for anchoring → unload jack, where σcon is the control stress, which refers to the maximum stress value controlled to be reached when the prestressed steel is tensioned.
[0018] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.
Claims
1. A method for secondary tensioning of prestressed steel strands of a lower deck girder of a double-deck bridge, characterized in that: Includes the following steps: S10. Installation of corrugated pipe: A positioning frame is installed along the length of the lower cap beam. The positioning frame avoids the upper pier column, and the center of the positioning frame coincides with the design center of the lower cap beam duct. Insert the corrugated pipe section by section from one end of the cap beam to the other, and secure the corrugated pipe and the positioning frame firmly. Anchor plates are installed on the end formwork of the cap beam, with the anchor holes of the anchor plates aligned with the ends of the corrugated pipes, and the anchor holes are sealed. S20, steel strand bundle: The cutting length L of the steel strand is equal to the actual length of the duct, the length reserved for tensioning at both ends, and the length clamped by the tool anchor. After the material is cut, use a tool to anchor and comb the bundle, and use an angle grinder to cut off the outer 30-50cm of the steel wire at the end of the steel strand, leaving one steel wire in the middle. Number each steel strand and mark the working anchor in the same way. Fix the remaining steel wire to the traction screw plug, and tie the end with tape. Finally, use a winch to pull the steel strand to complete the bundling. S30, Tensioning Platform Installation: The tensioning platform adopts a steel truss hanging basket structure, and the whole is a counterweight structure. In the area on the top surface of the cap beam that is not covered by the upper structure, the tensioning platform is fixed by truss ballast to keep the tensioning platform in balance. S40. Install the working anchor: Align the working anchor plate with the holes on the steel strands, ensuring that each steel strand is centered in the hole and does not rub against the hole wall. Then push the working anchor plate inward to make it fit tightly against the flared opening of the anchor plate. S50, pre-tensioning of steel strand: Install working clamps on one side of the steel strand and extension sleeves, jacks, tool anchors, and tool clamps on the other side. Tension twice at 15% of the control stress under the anchor. S60. Install the jack: Install working clamps at both ends of the steel strand, tighten the clamps with support nuts, and then install tool anchors and jacks on both sides of the steel strand. S70, tensioning: The steel strand is tensioned by jacks on both sides until the prestress test under the anchor is qualified; S80, Finishing: Dismantling the tensioning platform: Grouting is performed from one end of the duct until the other end of the duct is full and the cement grout discharged from the injection hole has the same required fluidity. The grout is continuously sprayed out and the consistency is similar to that of the injected grout. Cut off the exposed steel strands and seal the anchor head with cement grout.
2. The method for secondary tensioning of prestressed steel strands in the lower cap beam of a double-layer bridge according to claim 1, characterized in that: In step S60, the working anchor, working clamp, tool anchor, jack, and steel strand are concentric.
3. The method for secondary tensioning of prestressed steel strands in the lower cap beam of a double-layer bridge according to claim 1, characterized in that: In step S70, the tensioning of the prestressed steel strand adopts dual control of tension force and elongation, and the elongation is used for verification. The control stress under the anchor is 0.70fpk=1302Mpa.
4. The method for secondary tensioning of prestressed steel strands in the lower cap beam of a double-layer bridge according to claim 1, characterized in that: In step S70, the prestressed steel strand tensioning operation procedure is as follows: 0 → 15%σcon → 30%σcon → 50%σcon → return to 0 for inverted top → 50%σcon → 100%σcon → hold load for 10 minutes → oil cylinder return for anchoring → unload jack.
5. The method for secondary tensioning of prestressed steel strands in the lower cap beam of a double-deck bridge according to claim 1, characterized in that: In step S80, an abrasive wheel is used to cut the exposed steel strands.
6. The method for secondary tensioning of prestressed steel strands in the lower cap beam of a double-deck bridge according to claim 1, characterized in that: In step S30, the tensioning platform includes a platform frame, columns and trusses. The trusses are cantilevered on the cap beam. The platform frame is installed on the outer end of the truss through the columns. Steel plates are laid inside the platform frame. A counterweight bracket is set at the inner end of the truss. The counterweight bracket is fixed to the top surface of the cap beam by counterweight blocks.