Bridge full support preloading method and large-span bridge upper pre-stressed concrete box girder cast-in-situ construction method

Abstract

The application discloses a bridge full-support pre-pressing method and a large-span bridge upper pre-stressed concrete box girder cast-in-situ construction method, wherein a theoretical pre-pressing load value is calculated, an actual load pressure applied by an observation point on a side formwork in a vertical stress direction is derived according to an inclination angle of a surface where the observation point is located relative to a horizontal plane, and the pre-pressing pressure of a hydraulic jack is adjusted according to the actual load pressure value, so that the pre-pressing pressure of the hydraulic jack applied to the full-support is more close to the actual load pressure of the observation point, and the real bearing capacity of the support is more directly reflected.

Description

Technical Field

[0001] This invention relates to the field of bridge construction technology, specifically to a method for prestressing a full-span scaffold for bridges and a method for cast-in-place construction of prestressed concrete box girders for long-span bridges. Background Technology

[0002] The preloading of the support structure is mainly to verify its stability and obtain data on its deformation and ground settlement. Its purpose is to eliminate the inelastic deformation of the support structure (piers) and the foundation, and to obtain the elastic deformation value of the support structure (piers) as a basis for the construction camber. Measuring the ground settlement provides empirical data for the construction of similar bridges.

[0003] Among existing methods for preloading scaffolding, the commonly used methods include the sandbag method, the rebar stacking method, and the water tank method. These methods involve hoisting sandbags, stacking rebar, or stacking a set of water tanks onto the bottom formwork of the scaffolding, and then gradually loading and unloading according to design requirements to eliminate inelastic deformation and measure the elastic deformation of the scaffolding. In addition, to address the problems of long time, high difficulty, and high stacking height associated with these traditional methods, existing preloading methods also include the reverse preloading method using hydraulic jacks. For example, utility model patent CN202000264U describes a preloading system for bridge beam full-span scaffolding construction. This system involves setting anchors directly below the full-span scaffolding and placing a preloading unit consisting of hydraulic jacks and vertical tie rods between the full-span scaffolding and the anchors; this method replaces the existing methods of using sandbags, rebar, or water tanks for preloading.

[0004] The current pre-stressing method for full-span scaffolding involves first erecting horizontal, vertical, and diagonal tension scaffolding, then installing adjustable top supports on the top of the scaffolding. By adjusting the height of the top supports, the scaffolding supports the inclined or curved flanges on both sides of the concrete box girder. After that, bottom and side formwork are laid on top of the full-span scaffolding, and then the scaffolding is pre-stressed.

[0005] During preloading, measuring points are selected at equal intervals on the bottom and side formwork sections, with 5-7 measuring points selected on the same section. Typically, at least 3 measuring points are selected on the bottom formwork and at least 2 on the side formwork on the same cross-section. For the aforementioned reverse preloading method using hydraulic jacks, the hydraulic jacks are placed on the bottom formwork of the full-span scaffold, with the hydraulic jacks and vertical tie rods aligned vertically. However, for measuring points on inclined or curved side formwork, it is difficult to ensure the central axis of the hydraulic jacks is aligned vertically with the vertical tie rods. This leads to a discrepancy between the preloading pressure of the jacks and the actual load pressure at the measuring points, failing to reflect the true bearing capacity of the scaffold. This results in a significant difference between theoretical calculations and actual usage data, posing a safety hazard. Summary of the Invention

[0006] To address the aforementioned drawbacks, one objective of this invention is to provide a method for preloading a full-span scaffolding for bridges.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows:

[0008] The prestressing method for full-span scaffolding of bridges includes the following steps:

[0009] S1. Lay square timber and bottom formwork on the part corresponding to the main beam on the full-span scaffolding, and erect wing plate arc steel pipes and side formwork on the top of both sides of the full-span scaffolding.

[0010] S2. Set up observation points above the bottom template and side template. The observation points are set at the 1 / 2, 1 / 4 and middle sections of the 0# block of each span. Multiple observation points are set on each section and each observation point is numbered (i = 1, 2, 3Λn).

[0011] S3. Install a preloading system at the observation point. The preloading system includes a hydraulic jack and a vertical tie rod. At the observation point of the side formwork, the preloading system also includes a leveling pad. The hydraulic jack is installed above the leveling pad. The hydraulic jack and the vertical tie rod are on the same vertical axis.

[0012] S4. Detect the inclination α of the plane where each observation point on the side template is located, and calculate the theoretical preload P of each stage of the support. i (i = 1, 2, 3...n), the actual preload F is derived based on geometric relationships. i :

[0013] F i =P i *cosα;

[0014] S5. During preloading of the support structure, the preloading system is anchored, and the actual preloading load is applied by hydraulic jacks. This load is transmitted downwards through the force transmission system and evenly distributed across the full-span support structure. The actual preloading load F is applied by adjusting the pressure gauge reading. i (i = 1, 2, 3...n);

[0015] S6. After each level of preloading is completed, obtain the monitoring data of each observation point of the full-span scaffold under each level of preloading and analyze the results.

[0016] Furthermore, the hydraulic jacks are respectively fixed on the leveling pads on the bottom template and side template of the full-span scaffold, and the bottom end of the vertical tie rod is connected to the stable base at the bottom of the full-span scaffold, and its top end passes through the axial channel of the hydraulic jack.

[0017] Furthermore, the leveling pad includes a platform block and a plurality of adjustable supports below it. The bottom end of the adjustable supports is fixedly connected to the side template, and its top end is connected to the lower surface of the platform block. The level of the platform block can be adjusted by adjusting the different heights of the plurality of adjustable supports.

[0018] The second objective of this invention is to provide a method for the cast-in-place construction of prestressed concrete box girders for long-span bridges, comprising the following steps:

[0019] (1) Foundation treatment and scaffolding erection;

[0020] (2) Erect the main beam formwork and tie the main beam reinforcement;

[0021] (3) Cast the main beam concrete on site;

[0022] (4) Tension the prestressed steel strands and seal the anchors, then lower the frame;

[0023] After the scaffolding is erected, the bridge full-span scaffolding is preloaded according to the preload method described above.

[0024] Furthermore, in step (1) of the scaffold construction, the preload of the scaffold is not less than 110% of the total weight of the main beam and the formwork; when erecting the scaffold, allow for the elastic and inelastic deformation of the scaffold.

[0025] Furthermore, in step (2), all intersections of the bridge deck reinforcement bars should be tied to prevent the reinforcement bars from shifting during concrete pouring; when the center distance between the reinforcement bars in both directions is less than 300mm, they can be tied at every other intersection; the longitudinal welding of the reinforcement bars can be done by flash butt welding; when flash butt welding is not possible, arc welding (butt welding, lap welding) should be used.

[0026] Furthermore, precast concrete spacers are installed on the main beam formwork to ensure that the reinforcing bars are fixed in the correct position. The strength of the concrete in the spacers must be consistent with the strength of the adjacent concrete, and the spacing between the precast concrete spacers must not exceed 1.2m in both the longitudinal and transverse directions.

[0027] Furthermore, the joints of the reinforcing bars must be staggered. When the joints of the reinforcing bars are lapped by arc welding, the lapped ends of the two reinforcing bars should be folded to one side in advance to make the axes of the two joined reinforcing bars consistent. The length of the double-sided weld of the joint should not be less than 5d, and the length of the single-sided weld should not be less than 10d (d is the diameter of the reinforcing bar).

[0028] Furthermore, in step (3), the concrete should be poured in layers according to a certain thickness, sequence and direction. The upper layer of concrete should be poured before the lower layer of concrete has initially set or can be reshaped. When the upper and lower layers are poured at the same time, the distance between the upper and lower layers should be more than 1.5m. When pouring concrete on an inclined surface, it should be expanded and raised layer by layer from the lowest point, and the layers should be kept horizontal.

[0029] During the concrete pouring process, the deformation and settlement of the arch frame and supports are measured and recorded at any time.

[0030] The beneficial effects of this invention are as follows:

[0031] In this invention, the theoretical preload value is calculated, and the actual load pressure applied to the observation point in the vertical force direction on the side template is derived based on the inclination angle of the observation point relative to the horizontal plane. The preload pressure of the hydraulic jack is adjusted according to the actual load pressure value so that the preload pressure applied by the hydraulic jack to the full-span support is closer to the actual load pressure at the observation point, and the true bearing capacity of the support is reflected more intuitively. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the preloading system for the full-span scaffold in this invention.

[0033] In the diagram, 1. bottom formwork; 2. side formwork; 3. observation point; 4. hydraulic jack; 5. vertical tie rod; 6. leveling pad; 7. stable base; 8. platform block; 9. adjustable support; 10. full-span scaffold. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Other embodiments obtained by those skilled in the art based on the embodiments of this invention without conducting groundbreaking research are all within the scope of protection of this invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0035] Example 1

[0036] The prestressing method for full-span scaffolding of bridges includes the following steps:

[0037] S1. Lay square timber and bottom formwork 1 on the part corresponding to the main beam on the full-span scaffold 10, and erect wing plate arc steel pipe and side formwork 2 on the top of both sides of the full-span scaffold 10.

[0038] S2. Set up observation points above the bottom template and side template. The observation points are set at the 1 / 2, 1 / 4 and middle sections of the 0# block of each span. Multiple observation points are set on each section and each observation point is numbered (i = 1, 2, 3Λn).

[0039] Specifically, such as Figure 1As shown, for the selection of observation point 3 on the cross section, four measuring points can be equally spaced at both ends and the middle of the bottom template 1 near the side template 2, and four measuring points can be distributed at the positions of both sides of the side template 2 near their ends.

[0040] S3. Install a preloading system at observation point 3. The preloading system includes a hydraulic jack 4 and a vertical tie rod 5. At the observation point 3 of the side template 2, the preloading system also includes a leveling pad 6. The hydraulic jack 4 is installed above the leveling pad 6. The hydraulic jack 4 and the vertical tie rod 5 are on the same vertical axis.

[0041] The hydraulic jacks 4 are respectively fixed on the leveling pads 6 on the bottom template 1 and side template 2 of the full-span support 10. The bottom end of the vertical tie rod 5 is connected to the stable base 7 at the bottom of the full-span support 10, and its top end passes through the axial channel of the hydraulic jack 4.

[0042] The stable base 7 is firmly connected and fixed to the foundation of the scaffolding. Specifically, the stable base 7 can be made of concrete or fixed to the foundation by reinforcing bolts.

[0043] The specifications of the vertical tie rod 5 can be selected according to the needs, such as HRB400 or HPB300, as long as the pre-compression requirements are met and the tensile strength is exceeded to prevent breakage. If the frame is high, the vertical tie rod 5 can be extended by lap welding, electroslag pressure welding or mechanical sleeve connection. The specific method is not limited in this invention.

[0044] The leveling pad 6 includes a platform block 8 and a plurality of adjustable supports 9 below it. The bottom end of the adjustable support 9 is fixedly connected to the side template 2, and its top end is connected to the lower surface of the platform block 8. The level of the platform block 8 can be adjusted by adjusting the different heights of the plurality of adjustable supports 9.

[0045] Specifically, the adjustable support 9 can be set using hydraulic telescopic rods. Hydraulic telescopic rods are set at the four corners of the platform base. By adjusting the height of different hydraulic telescopic rods, the horizontal state of the platform block 8 can be adjusted so that the hydraulic jack 4 and the vertical tie rod 5 are kept on the same vertical line.

[0046] S4. Detect the inclination α of the plane where each observation point on the side template is located, and calculate the theoretical preload P of each stage of the support. i (i = 1, 2, 3...n), the actual preload F is derived based on geometric relationships. i :

[0047] F i =P i *cosα;

[0048] S5. During preloading of the support structure, the preloading system is anchored, and the actual preloading load is applied by hydraulic jacks. This load is transmitted downwards through the force transmission system and evenly distributed across the full-span support structure. The actual preloading load F is applied by adjusting the pressure gauge reading. i (i = 1, 2, 3...n);

[0049] S6. After each load preloading is completed, obtain the monitoring data of each observation point 3 of the full-span scaffold 10 under each level of preloading load and analyze the results.

[0050] In this invention, the theoretical preload value is calculated. Based on the inclination angle of the observation point 3 relative to the horizontal plane, the actual load pressure applied to the observation point 3 on the side template 2 in the direction of vertical force is derived. The preload pressure of the hydraulic jack 4 is adjusted according to the actual load pressure value so that the preload pressure applied by the hydraulic jack 4 to the full-span support 10 is closer to the actual load pressure of the observation point 3, and more intuitively reflects the true bearing capacity of the support.

[0051] Example 2

[0052] A method for cast-in-place construction of prestressed concrete box girder superstructure of long-span bridges includes the following steps:

[0053] (1) Foundation treatment and erection of supports; after the supports are erected, the bridge full-span supports 10 are preloaded according to the preloading method described in Example 1.

[0054] During scaffolding construction, the preload on the scaffolding is no less than 110% of the total weight of the main beam and the formwork; allowance is made for elastic and inelastic deformation of the scaffolding when it is erected.

[0055] (2) Erect the main beam formwork and tie the main beam reinforcement; all intersections of the bridge deck reinforcement should be tied to prevent the reinforcement from shifting when pouring concrete; when the center distance of the reinforcement in both directions is less than 300mm, the reinforcement can be tied every other intersection; the longitudinal welding of the reinforcement can be done by flash butt welding; when flash butt welding is not possible, arc welding (butt welding, lap welding) should be used.

[0056] Precast concrete spacers are installed on the main beam formwork to ensure that the reinforcing bars are fixed in the correct position. The strength of the concrete in the spacers must be consistent with the strength of the adjacent concrete. The spacing between the precast concrete spacers shall not exceed 1.2m in both the longitudinal and transverse directions.

[0057] Furthermore, the joints of the reinforcing bars must be staggered. When the joints of the reinforcing bars are lapped by arc welding, the lapped ends of the two reinforcing bars should be folded to one side in advance to make the axes of the two joined reinforcing bars consistent. The length of the double-sided weld of the joint should not be less than 5d, and the length of the single-sided weld should not be less than 10d (d is the diameter of the reinforcing bar).

[0058] (3) Cast the main beam concrete on site; the concrete should be poured in layers according to a certain thickness, sequence and direction. The upper layer of concrete should be poured before the lower layer of concrete has initially set or can be reshaped; when the upper and lower layers are poured at the same time, the distance between the upper and lower layers should be more than 1.5m; when pouring concrete on an inclined surface, it should be started from the lowest point and gradually expanded and raised, maintaining horizontal layering.

[0059] During the concrete pouring process, the deformation and settlement of the arch frame and supports are measured and recorded at any time.

[0060] (4) Tension the prestressed steel strands and seal the anchor, then lower the frame.

[0061] The technical solution of the present invention has been described in conjunction with the preferred embodiments of the examples. Those skilled in the art will readily understand that the above description is only a part of the embodiments of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements 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 preloading a bridge full-span scaffold, characterized in that, Includes the following steps: S1. Lay square timber and bottom formwork on the part corresponding to the main beam on the full-span scaffolding, and erect wing plate arc steel pipes and side formwork on the top of both sides of the full-span scaffolding. S2. Set up observation points above the bottom and side formwork. The observation points are located at the 1 / 2, 1 / 4 and middle sections of block #0 in each span. Multiple observation points are set on each section, and each observation point is numbered. ; S3. Install a preloading system at the observation point. The preloading system includes a hydraulic jack and a vertical tie rod. At the observation point of the side formwork, the preloading system also includes a leveling pad. The hydraulic jack is installed above the leveling pad. The hydraulic jack and the vertical tie rod are on the same vertical axis. S4. Inspect the inclination of the surface where each observation point is located on the side template. Calculate the theoretical preload of each stage of the support. The actual preload was derived based on geometric relationships. : ; S5. During preloading of the support structure, the preloading system is anchored, and the actual preloading load is applied by hydraulic jacks. This load is transmitted downwards through the force transmission system and evenly distributed across the full-span support structure. The actual preloading load is applied by adjusting the pressure gauge readings. ; S6. After each load preloading is completed, obtain the monitoring data of each observation point of the full-span scaffold under each load preloading level and analyze the results; The hydraulic jacks are respectively fixed on the leveling pads on the bottom template and side template of the full-span scaffold. The bottom end of the vertical tie rod is connected to the stable base at the bottom of the full-span scaffold, and its top end passes through the axial hole of the hydraulic jack and is fixed by bolts. The leveling pad includes a platform block and multiple adjustable supports below it. The bottom end of the adjustable supports is fixedly connected to the side template, and its top end is connected to the lower surface of the platform block. The level of the platform block can be adjusted by adjusting the different heights of the multiple adjustable supports.

2. A method for cast-in-place construction of prestressed concrete box girder superstructure of a long-span bridge, characterized in that, Includes the following steps, (1) Foundation treatment and scaffolding erection; (2) Erect the main beam formwork and tie the main beam reinforcement; (3) Cast the main beam concrete on site; (4) Tension the prestressed steel strands and seal the anchors, then lower the frame; After the scaffolding is erected, the bridge full-span scaffolding is preloaded according to the preloading method described in claim 1.

3. The method for cast-in-place construction of prestressed concrete box girder superstructure of a long-span bridge according to claim 2, characterized in that, In step (1) of the scaffold construction, the preload of the scaffold is not less than 110% of the total weight of the main beam and the formwork; when erecting the scaffold, allow for the elastic and inelastic deformation of the scaffold.

4. The method for cast-in-place construction of prestressed concrete box girder superstructure of a long-span bridge according to claim 2, characterized in that, In step (2), all intersections of the bridge deck reinforcement bars should be tied to prevent the reinforcement bars from shifting during concrete pouring; when the center distance between the reinforcement bars in both directions is less than 300mm, they can be tied at every other intersection; the longitudinal welding of the reinforcement bars can be done by flash butt welding; when flash butt welding is not possible, arc welding should be used.

5. The method for cast-in-place construction of prestressed concrete box girder superstructure of a long-span bridge according to claim 4, characterized in that, Precast concrete spacers are installed on the main beam formwork to ensure that the reinforcing bars are fixed in the correct position. The strength of the concrete in the spacers must be consistent with the strength of the adjacent concrete. The spacing between the precast concrete spacers shall not exceed 1.2m in both the longitudinal and transverse directions.

6. The method for cast-in-place construction of prestressed concrete box girder superstructure of a long-span bridge according to claim 4, characterized in that, Rebar joints must be staggered. When lap arc welding is used for rebar joints, the lap ends of the two rebars should be folded to one side in advance to make the axes of the two joined rebars consistent. The length of the double-sided weld of the joint should not be less than 5d, and the length of the single-sided weld should not be less than 10d, where d is the diameter of the rebar.

7. A method for cast-in-place construction of prestressed concrete box girder superstructure of a long-span bridge according to claim 2, characterized in that, In step (3), the concrete should be poured in layers according to a certain thickness, sequence and direction. The upper layer of concrete should be poured before the lower layer of concrete has initially set or can be reshaped. When the upper and lower layers are poured at the same time, the distance between the upper and lower layers should be more than 1.5m. When pouring concrete on an inclined surface, it should be expanded and raised layer by layer from the lowest point, and the layers should be kept horizontal. During the concrete pouring process, the deformation and settlement of the arch frame and supports are measured and recorded at any time.

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