Synchronous Tensioning Construction Technology for Continuous Rigid Frame Cantilever

Abstract

The present invention relates to a construction technology for synchronous tensioning of cantilevers of continuous rigid frames, comprising the following steps: S1 installing prestressed ducts on concrete; S2 fabricating prestressed steel tendons and placing the prestressed steel tendons into the prestressed ducts; S3 preparing the anchorages, stretching machines and intelligent tensioning systems, and symmetrically tensioning the prestressed steel tendons at both ends. In this step, marks are made on the prestressed steel tendons between the anchorages and the stretching machines to form a marked surface, and an image processing device is connected to the intelligent tensioning system, and the image processing device can collect images of the marked surface; when the image processing device detects that the size of the marked surface changes along the axial direction of the prestressed steel tendon, the elongation is recorded; S4 recording the oil gauge readings and the elongation. The present invention can tension the beam segments in place, better reinforce the beam segments, and make the cracks and deformations of the continuous rigid frame bridge appear as late as possible.

Description

Technical Field

[0001] The invention relates to the field of building construction, and in particular to a continuous rigid frame cantilever synchronous tensioning construction process. Background Art

[0002] Continuous steel structure has been developed rapidly in recent years and widely used on highways due to its advantages of beam continuity, beam pier consolidation and convenient construction. At present, the span of continuous steel structure is increasing. The design of Fengjie Yangtze River Bridge with a span of 280 meters is underway. In the Mendong Channel Bridge project of Lingdingyang Channel, a continuous steel structure with a span of 318 meters has been proposed.

[0003] Among them, prestressed tensioning construction is the core of continuous steel structure construction. The cantilever casting of continuous rigid frame bridges usually adopts symmetrical tensioning at both ends. In order to make the tensioning force control more accurate, the "double control method" of stress and strain is generally adopted, with stress control (oil gauge reading control) as the main control and strain control (elongation control) as the auxiliary control. Prestressed pipes are installed on the beam sections, and prestressed steel bundles are placed in the prestressed pipes. Tensioning equipment is set on the prestressed steel bundles to directly tension the prestressed steel bundles at both ends.

[0004] However, the applicant found that when many beam sections were tensioned symmetrically at both ends, even if the stress-strain control met the requirements of the "double control method", cracks and deformations of varying degrees would occur during normal use. Therefore, the applicant believes that the current tensioning construction technology still has room for improvement to better reinforce the beam sections. Summary of the invention

[0005] The present invention is intended to provide a continuous rigid frame cantilever synchronous tensioning construction process to solve the problem of early occurrence of cracks and deformation in current continuous steel structure bridges.

[0006] In order to achieve the above object, the present invention adopts the following technical scheme:

[0007] A continuous rigid frame cantilever synchronous tensioning construction process comprises the following steps:

[0008] S1 installs prestressed pipes on concrete;

[0009] S2 prestressed steel strands are manufactured and placed in prestressed pipes;

[0010] Prepare the S3 anchor, tensioning machine and intelligent tensioning system, and symmetrically tension the prestressed steel strand at both ends. In this step, mark the prestressed steel strand between the anchor and the tensioning machine to form a marked surface, connect the image processing device to the intelligent tensioning system, and the image processing device can collect images of the marked surface; when the image processing device detects that the size of the marked surface does not change along the axial direction of the prestressed steel strand, the intelligent tensioning system does not record the elongation; when the image processing device detects that the size of the marked surface changes along the axial direction of the prestressed steel strand, start recording the elongation;

[0011] S4 Record the oil gauge reading and elongation;

[0012] The applicant has found that when symmetrically tensioning both ends of the beam segment, due to the large transverse and longitudinal dimensions of the beam segment, the prestressed steel strand passing through the prestressed duct is long and heavy, and it is very difficult to ensure that the prestressed steel strand is in a straight state. Therefore, the prestressed steel strand in the prestressed duct is inevitably in a bent state. If the prestressed steel strand is directly tensioned at both ends, at this time, what the intelligent tensioning system records is not the elongation, but the straightening amount, that is to say, the prestressed steel strand does not undergo elastic deformation but is regarded as having undergone deformation, which leads to inaccurate tensioning data, especially the elongation, and there is a possibility that the beam segment is not tensioned in place.

[0013] The advantages of this solution are:

[0014] 1. By judging the deformation of the marked surface along the axial direction of the prestressed steel strand, it is determined whether the prestressed steel strand has undergone elastic deformation. Only when elastic deformation occurs is the actual elongation (not the straightening amount), and the elongation will be recorded, so that the recording of the elongation is more accurate, the control of the tensioning is more effective, and the possibility that the beam segment is not tensioned in place is reduced.

[0015] 2. The image processing device is used in cooperation with the intelligent tensioning system to reflect the deformation of the marked surface along the axial direction of the prestressed steel strand through image changes. The existing image acquisition technology can be used to efficiently and timely detect the deformation of the marked surface along the axial direction of the prestressed steel strand, and automatic control can be achieved, avoiding the errors caused by manual operation.

[0016] The present invention can tension the beam segment in place, better reinforce the beam segment, and make the cracks and deformations of the continuous rigid frame bridge appear as late as possible.

[0017] Optionally, the edge of the marked surface is linear. In this way, the boundary of the edge of the marked surface is clearer, the difficulty of image change recognition is reduced, and the detection of the marked surface by the image processing device is more accurate.

[0018] Optionally, the marked surface is coated with spray paint. When spray painting, a spray painting template can be used in cooperation to form a marked surface with a standardized and clear boundary, ensuring the accuracy of the deformation detection of the marked surfaces under multiple tensionings.

[0019] Optionally, the length of the marked surface is greater than 1 cm. The length is not too short, which is more convenient for detecting the deformation of the marked surface along the axial direction of the prestressed steel strand.

[0020] Optionally, in order to eliminate the inelastic deformation of the prestressed steel strand as much as possible, ensure that each prestressed steel strand is in a straightened stress state after the initial stress is applied, and make the actual elongation closer to the theoretical elongation. When the prestressed steel strand is greater than 60 m, the initial tensioning stress is 25% of the designed tensioning stress value, and the holding time is 5 min.

[0021] Optionally, in order to eliminate the inelastic deformation of the prestressed steel strand as much as possible, ensure that each prestressed steel strand is in a straightened stress state after the initial stress is applied, and make the actual elongation closer to the theoretical elongation. When the prestressed steel strand is greater than 30 m and less than or equal to 60 m, the initial tensioning stress is 15% - 20% of the designed tensioning stress value, and the holding time is 5 min.

[0022] Optionally, it further includes a remote data management system for receiving the data of the intelligent tensioning system. The data between the remote data management system and the intelligent tensioning system is transmitted wirelessly, and the distance does not exceed 2 km. The network at the construction site is often not smooth, so the tensioning data is backed up through a dedicated network server. The wireless transmission distance should not be too long, otherwise it is difficult to ensure that the data of the intelligent tensioning system is transmitted to the remote data management system safely and at high speed. Specific embodiments

[0023] The following is a further detailed description through specific embodiments:

[0024] A continuous rigid frame cantilever synchronous tensioning construction process, taking the longitudinal prestressing construction as an example, includes the following steps:

[0025] S1 Install longitudinal prestressed ducts on the concrete, and the length of the ducts is 50 m;

[0026] S2 Fabricate the prestressed steel strands and place the prestressed steel strands in the prestressed ducts: Set positioning steel bars for positioning, with one positioning bar every 0.8 m in the straight section and one positioning bar every 0.5 m in the curved section. A plastic lining tube is inserted into the duct to keep the duct straight. The diameter of the lining tube is generally 1 cm smaller than the diameter of the duct. During the concrete pouring process, the lining tube is often rotated to prevent the prestressed corrugated pipe from leaking and "freezing" the lining tube. After the concrete pouring is completed and the initial setting occurs, the lining tube is withdrawn. The longitudinal prestressed steel strands are threaded through the ducts by a strand threading machine and pulled as a whole by a winch for threading long strands.

[0027] Prepare the S3 anchor, stretching machine and intelligent tensioning system, and perform symmetric tensioning at both ends of the prestressed steel strand. The intelligent tensioning system has been disclosed in the invention patent with the publication number of CN 102031874 B. In actual use, it does not rely on manual control, but uses computer intelligent control technology to automatically operate through instruments to complete the tensioning construction of the steel strand.

[0028] Main technical indicators of intelligent tensioning: the accuracy of the force measuring system is 1% FS, the displacement measurement accuracy is 0.2 mm, the unbalance of the double-top opposite tension is 20 kN, the wireless transmission distance is 2 km, the working voltage of the hydraulic station is 380 ± 10% V, and the working voltage of the control system is 220 ± 10% V. To ensure the reliability of the tensioning data, triple protection is adopted:

[0029] ① The tensioning data is stored in real time through a dedicated on-site memory.

[0030] ② The tensioning data is transmitted into the information management system in an infinite way through the communication interface, and the tensioning data, the tension force curve and the elongation curve can be displayed in real time, and local recording and storage are carried out at the same time.

[0031] ③ Remote data management system: Back up the tensioning data through a dedicated network server, and reproduce and display the tensioning data, the tension force curve and the elongation curve through a dedicated program.

[0032] Intelligent tensioning has many advantages compared with traditional tensioning. The tensioning data ensures accuracy, which is beneficial to the prestressed force of the structure, and the cost is greatly reduced. The comparison between traditional manual tensioning and intelligent tensioning is shown in Table 1:

[0033]

[0034]

[0035] Table 1

[0036] In this step, it is also necessary to mark the prestressed steel strand between the anchor and the stretching machine to form a marking surface. The marking surface is a 15 mm * 5 mm (length * width) rectangle that is bent along the radial direction of the prestressed steel strand. The axis of symmetry of the rectangle is parallel to the axis of the prestressed steel strand. The length direction of the marking surface is the same as the axial direction of the prestressed steel strand. The marking surface is coated with paint using a paint spraying mold with a rectangular opening. Connect the image processing device to the intelligent tensioning system, and the camera of the image processing device can collect images of the marking surface; when the processing module of the image processing device detects that the size of the marking surface does not change along the axial direction of the prestressed steel strand, the intelligent tensioning system does not record the elongation; when the processing module of the image processing device detects that the size of the marking surface changes along the axial direction of the prestressed steel strand, the elongation is recorded.

[0037] The first tension stress is 20% of the designed tension stress value, and the holding time is 5 minutes. The second tension stress is 50% of the designed tension stress value, and the third tension stress is 100% of the designed tension stress value.

[0038] S4 Records the oil gauge reading and elongation, and forms a tension curve and an elongation curve.

[0039] S4 Duct grouting. At one end of the prestressed duct, a vacuum pump is used to evacuate the duct to make the duct reach a vacuum degree of about -0.1 MPa. Then, at the other end of the prestressed duct, a grouting machine is used to press the cement slurry into the prestressed duct with a positive pressure of ≥0.7 MPa, so as to improve the fullness and density of the prestressed duct grouting, and reduce the influence of air bubbles and moisture on the prestressed steel bundle.

[0040] During the tension construction process, the applicant found that 90% of the beam segments were in a straightened state before the end of the first tension stress, and there was a slight deformation along the axial direction of the prestressed steel bundle on the marked surface. 10% of the beam segments were not straightened before the end of the first tension stress and were only in a straightened state during the second tension, and the marked surface began to slightly deform along the axial direction of the prestressed steel bundle after the second tension. For this situation, the elongation and the elongation curve were automatically corrected to make the tension data and the curve more accurate, so as to tension the beam segment in place, better reinforce the beam segment, and make the cracks and deformations of the continuous rigid frame bridge appear as late as possible.

[0041] The above are only embodiments of the present invention. Specific technical solutions and / or common knowledge such as characteristics well known in the art are not described in detail herein. It should be noted that for those skilled in the art, without departing from the technical solution of the present invention, several deformations and improvements can be made, which should also be regarded as the protection scope of the present invention, and these will not affect the implementation effect of the present invention and the practicability of the patent. The protection scope required by this application should be subject to the content of its claims, and the specific implementation manners and other records in the specification can be used to interpret the content of the claims.

Claims

1. A construction technology for synchronous tensioning of continuous rigid frame cantilevers, comprising the following steps: S1 Install prestressed ducts on the concrete; S2 Manufacture prestressed steel tendons and place the prestressed steel tendons in the prestressed ducts; S3 Prepare the anchor devices, tensioning machines and intelligent tensioning systems, and symmetrically tension the prestressed steel tendons at both ends; S4 Record the oil gauge readings and elongation; It is characterized in that In step S3, marks are made on the prestressed steel tendon between the anchor device and the tensioning machine to form a marked surface, and an image processing device is connected to the intelligent tensioning system. The image processing device can collect images of the marked surface; when the image processing device detects that the size of the marked surface does not change along the axial direction of the prestressed steel tendon, the intelligent tensioning system does not record the elongation. When the image processing device detects that the size of the marked surface changes along the axial direction of the prestressed steel tendon, the elongation recording starts.

2. The continuous rigid frame cantilever synchronous tensioning construction process according to claim 1, characterized in that: The edge of the marked surface is linear.

3. The continuous rigid frame cantilever synchronous tensioning construction process according to claim 2, characterized in that: The marked surface is coated with paint spraying.

4. The continuous rigid frame cantilever synchronous tensioning construction process according to claim 2, characterized in that: The length of the marked surface is greater than 1 cm.

5. The continuous rigid frame cantilever synchronous tensioning construction process according to claim 4, characterized in that: When the prestressed steel tendon is greater than 60 m, the initial tension stress is 25% of the designed tension stress value, and the holding time is 5 min.

6. The continuous rigid frame cantilever synchronous tensioning construction process according to claim 5, characterized in that: When the prestressed steel tendon is greater than 30 m and less than or equal to 60 m, the initial tension stress is 15% - 20% of the designed tension stress value, and the holding time is 5 min.

7. The continuous rigid frame cantilever synchronous tensioning construction process according to claim 5, characterized in that: It also includes a remote data management system for receiving data from the intelligent tensioning system. The remote data management system and the intelligent tensioning system use wireless transmission, and the distance does not exceed 2 km.

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