Cast-in-place construction method for oversized span mixed inverted-T-shaped bent cap truss type support

Abstract

The invention relates to a cast-in-place construction method for a super-large-span mixed inverted-T-shaped bent cap truss type support. The cast-in-place construction method comprises the following steps that S1, a bearing formwork support foundation is constructed; s2, mounting a hoop platform on a column body of the bearing column; s3, external prestressing systems are installed on the two opposite sides of the hoop platform; s4, mounting a connecting hoop; s5, supporting steel pipe sets are installed on the platform bodies on the two sides of the hoop platform; s6, truss girder installation; s7, two truck cranes are adopted to place the spliced truss girders on the transverse distribution girders; s8, a bottom die system used for pouring a bent cap is installed along the installed truss girder; s9, steel bar structural parts used in the bent cap are manufactured and formed through steel bars; s10, the bent cap is formed through secondary pouring, and an inverted-T-shaped bent cap is formed through pouring; s11, dismantling the truss girder; according to the construction method, the construction problem of the super-large-span cast-in-place prestressed concrete inverted-T-shaped bent cap is solved.

Description

Technical Field

[0001] This invention belongs to the field of engineering construction technology, and in particular relates to a method for cast-in-place construction of ultra-large span hybrid inverted T-shaped cap beam truss support. Background Technology

[0002] With urban development, urban land resources are becoming increasingly scarce. Existing roads and bridges often cannot meet the growing travel needs of the people, making the development of transportation systems into higher-level spaces and underground infrastructure an inevitable trend. Constructing elevated bridges (hereinafter referred to as "new bridges") above the projection surface of existing double-span separated bridges (hereinafter referred to as "old bridges") to alleviate existing traffic pressure is often a better option. Compared to building on newly acquired land, this method saves land resources and significantly reduces the hassles associated with land acquisition, such as house demolition, pipeline relocation, and adjustments to existing roads, thus saving substantial construction investment.

[0003] When constructing a new bridge above the projection surface of an old bridge, the underlying structure of the old bridge often needs to be preserved intact during construction. Due to space constraints imposed by the existing bridge, the bridge foundation and substructure often employ a three-column structure with a single pile and a single column (one pier on each side of the median strip and edge line of the two bridge spans). When the old bridge is wide, the span of the new bridge's cap beam increases accordingly, and the cross-section of the cap beam is adjusted from a conventional rectangle to an inverted T-shape to meet the crossing requirements. Considering the heavy self-weight of the cap beam structure (approximately 1253 tons) and the relatively weak load-bearing capacity of the old bridge, setting up temporary load-bearing formwork on the old bridge during construction poses a significant risk. Therefore, the temporary load-bearing formwork needs to span the old bridge laterally in one span, placing high demands on the strength, stiffness, and stability of the support structure. By employing our company's independently developed "a hybrid solid-web variable cross-section truss beam" and "an adjustable truss for hybrid solid-web variable cross-section truss beams," the problem of insufficient load-bearing capacity when using conventional 321, HD200, and XT300 type prefabricated Bailey beams or large-specification steel structure main beams was successfully solved.

[0004] Generally, when the cap beam is small, the pier cap beam is often constructed using a clamp + load-bearing formwork or a full-span scaffolding cast-in-place method. However, when the cap beam is heavy, the conventional clamp + load-bearing formwork cannot meet the load-bearing requirements, and setting up temporary piers with full-span scaffolding on the existing bridge poses a great risk. Therefore, it is necessary to develop a method for the cast-in-place construction of cap beams on existing bridges with ultra-large spans, as well as a method for the installation and dismantling of scaffolding. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a method for the on-site construction of ultra-large span hybrid inverted T-shaped cap beams with truss supports, thereby solving the construction problem of ultra-large span cast-in-place prestressed concrete inverted T-shaped cap beams.

[0006] The objective of this invention is achieved through the following technical solution: a method for in-situ construction of ultra-large span hybrid inverted T-shaped cap beam truss-type supports, which includes the following steps: S1. Construction of the load-bearing formwork foundation: pour a concrete cushion layer within the pile body of the cast-in-place pile and use it as a hoop platform layer, and cast the pile into shape to serve as a load-bearing column for the ultra-large span mixed inverted T-shaped cap beam. S2. Install a clamping platform on the column body of the load-bearing column, and place the clamping platform on the concrete pad. S3. Install an external prestressing system on both sides of the clamping platform; S4. Install connecting clamps: Install one connecting clamp every three meters along the height of the load-bearing column. S5. Supporting steel pipe assemblies are installed on both sides of the clamping platform. A longitudinal distribution beam and a transverse distribution beam are installed above the supporting steel pipe assembly. Limiting blocks are installed on the outer side of the transverse distribution beam, and the transverse distribution beam extends out of the outer side of the supporting steel pipe assembly. S6. Truss beam installation: Truss beam assembly jigs are used to assemble the beams on the ground. The jigs are equipped with two jigs, which are used to temporarily fix the end segments of the truss beams. The truss beams are configured and adjusted according to the overall length of the truss beams required on site and spliced ​​with the two end segments of the truss beams to form the final shape. S7. Two truck cranes are used to place the spliced ​​truss beams on the transverse distribution beams. Steel wedge-shaped adjustment blocks are installed between the transverse distribution beams and the truss beams, and are installed sequentially from the inner side to the outer side of the two opposite sides of the load-bearing columns. The two truss beams located on the inner side of the load-bearing columns are fixed by connecting frames, and the remaining adjacent truss beams are fixed by connecting plates. S8. Install the bottom formwork system for casting the cap beam along the installed truss beam; S9. Steel reinforcement structural components used inside the cap beam, formed by steel bars; S10. The cap beam is formed by two-stage casting and is cast into an inverted T-shaped cap beam. S11. Truss beam removal: First, remove the bottom formwork system, then remove the truss beam, and finally remove the clamp platform.

[0007] The beneficial effects of this invention are as follows: Compared with the prior art, the use of the column-supported ground-mounted cap beam formwork platform in steps S1-S3 fully utilizes the bearing capacity of the permanent structure, eliminates the need for large-scale foundation treatment, generates no solid waste, and has significant economic and environmental benefits. It successfully solves the difficulty of high requirements for foundation bearing capacity and rigidity of the cap beam formwork. Furthermore, through the installation of the supporting steel pipe assembly and truss beam in steps S4-S10, the construction of large-span inverted T-shaped cap beams is successfully achieved. And through the disassembly and assembly method in step S11, the truss beam can be smoothly disassembled and assembled.

[0008] Preferably, in step S1, the pile head of the cast-in-place pile is removed to the designed pile top elevation using a pneumatic hammer. If the concrete quality within the pile body area after removal to the pile top elevation is poor, the removal continues down to the fresh concrete surface. A 2.8m diameter C40 concrete layer is poured within 50cm of the pile bottom, and the top surface is reinforced with HRB400 Φ25 steel bars. The pile perimeter is backfilled with slag at least 1.0m thick in layers, with each layer less than 50cm thick and compacted. The road machinery compacted the soil, and after leveling the top of the quarry with fine quarry slag, a C30HRB400Φ16 reinforced concrete cushion layer was poured. After the cushion layer was poured, it was covered with geotextile for curing. The area around the pile is 6.6m long and 4.8m wide along the direction of the reinforced structure. Through the above-mentioned foundation treatment around the cast-in-place piles, i.e., the load-bearing columns, the ground-mounted hoop platform is supported. By setting the reinforced structure on the top surface of the cast-in-place piles, the foundation and the cast-in-place piles can share the bearing capacity, resulting in better bearing stability.

[0009] Preferably, in step S3, the external prestressing system is arranged in a relatively distributed manner along the length of the clamping platform and along the direction of the reinforcing bar structure. The external prestressing system is composed of supporting square timber, I-beams, and threaded steel bars. The supporting square timber is fixed on the clamping platform placement layer and located on the outside of the clamping platform. The elevation of the supporting square timber is the same as the design bottom elevation of the lowest layer of steel web of the clamping platform. The elevation of the uppermost layer is adjusted using wedge blocks. Then, the I-beams are installed sequentially, and each layer is spot-welded to the lower layer of I-beams. The distribution of the I-beams is such that their webs are arranged sequentially from bottom to top, with the top and bottom plates stacked. Threaded steel bars are inserted between adjacent I-beams, and the exposed lengths at both ends are adjusted to be consistent and the threaded steel bars are tightened. The threaded steel bars are located on both sides of the clamping platform in the width direction. By setting I-beams on the clamping platform and inserting and fixing prestressed threaded steel bars between the I-beams, the load-bearing capacity is greatly improved, the installation is simple, the safety and reliability are guaranteed, and the manufacturing is simple, without changing the structural design of the load-bearing platform, thereby improving the load-bearing capacity of the load-bearing platform.

[0010] Preferably, in step S5, each side of the supporting steel pipe group has five supporting steel pipes. Adjacent supporting steel pipes are connected by structural steel. Four supporting steel pipes are symmetrically distributed along the center of the clamp platform and close to the load-bearing column. The two supporting steel pipes on one side of the load-bearing column are connected and fixed to the connecting clamp on the load-bearing column by three structural steel. The third supporting steel pipe is located on the outermost side and forms a triangular distribution at the center point between the two supporting steel pipes. The height difference between the height of this supporting steel pipe and the height of the other four supporting steel pipes is the height of the longitudinal distribution beam. With the above structure, the length of the supporting steel pipes can be adjusted according to the actual height requirements of each cap beam to meet the erection height requirements. Through the arrangement of the connecting clamps and the five supporting steel pipes, the load-bearing capacity and verticality can be well controlled. The height of the longitudinal distribution beam is left between the supporting steel pipes, so that the transverse distribution beam can be adjusted horizontally and facilitates subsequent disassembly and assembly.

[0011] Preferably, the truss beams in steps S6 and S7 are hybrid solid-web variable cross-section truss beams, including two variable cross-section beams and several adjustable truss beams, which are rectangular cross-section beams. The several rectangular cross-section beams are arranged in a straight line and fixed to each other to form a truss. The two variable cross-section beams are located on both sides of the truss and fixed, and the variable cross-section beams are fixed to the columns. The truss spans across the existing bridge. Adjacent trusses are connected and fixed by connecting frames. Through the above structure, the truss is formed by several adjustable truss beams arranged in a straight line and fixed to each other, and two variable cross-section beams are located on both sides of the truss and fixed. It spans the existing bridge structure in one span, avoiding the need to set up temporary piers on the old bridge, reducing construction risks, and solving the shortcomings of traditional support structures such as small span capacity and weak load-bearing capacity. It has the advantages of high load-bearing capacity, high rigidity, and high stability without central support.

[0012] Preferably, the variable cross-section beam includes a solid-web member beam and a supporting member beam. The supporting member beam and the solid-web member beam are connected and fixed by welding. The solid-web member beam is fixed to the load-bearing column. The supporting member beam and the adjusting truss beam are connected and fixed by bolt assemblies. The cross-section of the supporting member beam is the same as that of the adjusting truss beam. With the above structure, compared with the existing all-solid-web structural beam, the self-weight is greatly reduced under the same working conditions, and the economy is higher.

[0013] Preferably, the adjustable truss beam includes an upper axial member and a lower axial member, which are symmetrically distributed. Both ends of the upper and lower axial members have adjusting bolt holes. Three equally spaced vertical web members and two diagonal web members are installed between the upper and lower axial members. The two diagonal web members are located between the three vertical web members and arranged in a "∧" shape. The junctions between the diagonal web members and the vertical web members are fixedly connected by a connecting plate, which is fixed to the lower end face of the upper axial member or the upper end face of the lower axial member. This structural arrangement, using upper and lower axial members and vertical web members and two diagonal web members between them, ensures strength and stability. The adjusting bolt holes at both ends of the upper and lower axial members allow for flexible combination with a mixed solid-web variable cross-section truss beam to adapt to installation requirements under various spans, offering greater flexibility in combination.

[0014] Preferably, the bottom formwork system in step S8 includes crossbeams and longitudinal beams. The crossbeams are sequentially spliced ​​along the length of the truss beam. Two longitudinal beams are installed on the crossbeams along the length of the truss beam, and the two longitudinal beams are located on both sides of the load-bearing column. Crossbeams, which are sequentially spliced ​​along the length of the truss beam, are installed on the two longitudinal beams, and square timber and bamboo plywood are laid on the crossbeams. Through the above structure, the two crossbeam structures improve the leveling of the bottom formwork system. At the same time, since the cap beam is designed with an inverted T-shape, the bottom width is greater than the top width, and the top width is the same as the load-bearing column. Therefore, the strength requirements of the bottom formwork system are very high. The support of the two crossbeam structures greatly enhances the support strength.

[0015] As a preferred method, in step S11, the bottom formwork system is first dismantled by adjusting the steel wedge-shaped adjustment blocks to symmetrically lower the beams by 5-10cm, and removing the square timber and bamboo plywood. The horizontal beams and longitudinal beams are then dismantled in sequence, leaving one horizontal beam connected to the flower rack intact as a spreader for dismantling the flower rack. Next, the truss beams are dismantled, and the connecting bolts between the flower rack and the truss beam are removed. A section of a hand-operated hoist is hung on the horizontal beam, and the flower rack is gradually lowered to the ground using the hand-operated hoist. The flower rack is then hoisted to the storage location using a truck crane. The connecting flower racks and the spreader of the transverse distribution beams are dismantled piece by piece. The truss beams outside the projection plane of the cap beam are dismantled using a truck crane and hoisted to a ground jig for storage or transported to the next work surface for installation. The high-strength bolts of the truss beam girders are not removed. Through the above dismantling method, the connecting flower racks can be dismantled using the existing structure, which is more convenient and has higher construction efficiency.

[0016] As a preferred option, in step S11, because the cap beam has an inverted T-shaped structure, part of the truss beam is located below the projection plane of the cap beam structure. Due to the limitations of on-site operating conditions, the truss beam needs to be moved below the projection plane of the structure before being dismantled using a truck crane. The dismantling process is as follows: Install jacks onto the lower transverse distribution beam of the truss beam, and adjust the jacking iron to be in close contact with the lower part of the truss beam. Use the jacks to slowly and synchronously lift the truss beam by about 3cm. Install the translation trolley and slowly and synchronously reset the jacks, so that the truss beam rests on the translation trolley. Finally, the jacks were removed, and the truss beams were moved to outside the projection plane of the cap beam. A truck crane was then used for dismantling, with the operation method being the same as for dismantling truss beams outside the projection plane of the cap beam. Finally, the clamping platform was removed, and the supporting steel pipe assemblies were dismantled sequentially from top to bottom, followed by the removal of the clamping platform. This dismantling method effectively solves the problem of dismantling truss beams within the projection plane of the cap beam due to the inverted T-shaped structure, which limits the dismantling of some truss beams below the cap beam's projection plane and restricts on-site working conditions. The dismantling is more stable and efficient. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of step S1 of the cast-in-place construction method of the present invention.

[0018] Figure 2 This is a schematic diagram of steps S2 and S3 of the cast-in-place construction method of the present invention.

[0019] Figure 3 This is a schematic diagram of step S4 of the cast-in-place construction method of the present invention.

[0020] Figure 4 This is a schematic diagram of step S5 of the cast-in-place construction method of the present invention.

[0021] Figure 5 This is a schematic diagram of step S5 of the cast-in-place construction method of the present invention.

[0022] Figure 6 This is a schematic diagram of step S6 of the cast-in-place construction method of the present invention.

[0023] Figure 7 This is a schematic diagram of step S7 of the cast-in-place construction method of the present invention.

[0024] Figure 8 This is a schematic diagram of step S7 of the cast-in-place construction method of the present invention.

[0025] Figure 9 This is a schematic diagram of steps S7 and S8 of the cast-in-place construction method of the present invention.

[0026] Figure 10 This is a schematic diagram of step S11 of the cast-in-place construction method of the present invention.

[0027] Figure 11This is a schematic diagram of step S11 of the cast-in-place construction method of the present invention.

[0028] Figure 12 This is a schematic diagram of step S11 of the cast-in-place construction method of the present invention.

[0029] Figure 13 This is a schematic diagram of the truss beam structure of the present invention.

[0030] Figure 14 This is a schematic diagram of the adjustable truss beam structure of the present invention.

[0031] The labels in the attached diagram are as follows: 1. Variable cross-section beam; 2. Adjustable truss beam; 3. Truss; 11. Solid web member beam; 12. Supporting member beam; 21. Upper axial member; 22. Lower axial member; 23. Adjusting bolt hole; 24. Vertical web member; 25. Diagonal web member; 26. Draping plate; 100. Hoop platform placement layer; 101. Load-bearing column; 102. Hoop platform; 103. External prestressing system; 104. Connecting hoop; 105. Supporting steel pipe assembly; 106. Longitudinal distribution beam; 107. Transverse distribution beam; 108. Limiting block; 109. Truss beam; 110. Assembly jig; 111. Steel wedge-shaped adjusting block; 112. Connecting pergola; 113. Bottom formwork system; 114. Cap beam; 115. Reinforced concrete structure; 116. Jack; 117. Translation trolley; 118. Concrete; 119. Slag layering; 103-1. Supporting square timber; 103-2. I-beam; 103-3. Threaded steel; 105-1. Supporting steel pipe; 105-2. Structural steel; 113-1. Crossbeam; 113-2. Longitudinal beam; 113-3. Square timber; 113-4. Bamboo plywood. Detailed Implementation

[0032] The invention will now be described in detail with reference to the accompanying drawings: as shown in the drawings Figures 1 to 12 As shown, the construction method of the present invention includes the following steps: S1. Construction of the load-bearing formwork foundation: pour a concrete cushion layer within the pile body of the cast-in-place pile and place it as a hoop platform layer 100, and cast the cast-in-place pile to form a load-bearing column 101 that serves as an ultra-large span mixed inverted T-shaped cap beam. S2. Install the clamp platform 102 on the column body of the load-bearing column 101, with the clamp platform 102 resting on the concrete pad. Specifically, the position of the clamp platform is marked on the concrete pad at the top of the pile according to the design location and marked with spray paint. A 25T crane is used to lift half of the clamp platform to the installation position, and then the two ear plates are tightened together with a wrench. The clamp connecting ear plates are connected into a whole using 10.9sM24 high-strength bolts, and finally, the external prestressing system is constructed. This makes the installation of the clamp platform 102 more accurate, stronger, and more efficient.

[0033] S3. Install an external prestressing system 103 on both sides of the clamping platform 102; S4. Install connecting clamps 104. Install one connecting clamp 104 every three meters along the height direction of the load-bearing column 101. S5. Supporting steel pipe assemblies 105 are installed on both sides of the clamping platform 102. A longitudinal distribution beam 106 and a transverse distribution beam 107 are installed above the supporting steel pipe assembly 105. A limit stop 108 is installed on the outer side of the transverse distribution beam 107, and the transverse distribution beam 107 extends out of the outer side of the supporting steel pipe assembly 105. S6. Truss beam 109 installation: The truss beam assembly frame is used to assemble the beams on the ground. The assembly frame 110 is equipped with two truss beams 109, which are used to temporarily fix the end segments of the truss beams 109. The truss beams 109 are configured and adjusted according to the overall length of the truss beams 109 required on site and spliced ​​with the two end segments of the truss beams 109 to form the final shape. S7. Two truck cranes are used to place the spliced ​​truss beams 109 on the transverse distribution beams 107. Steel wedge-shaped adjustment blocks 111 are installed between the transverse distribution beams 107 and the truss beams 109. If the height is insufficient, steel beams can be installed again, and they are installed sequentially from the inner to the outer sides of the two opposite sides of the load-bearing column 101. The two truss beams 109 located on the inner side of the load-bearing column 101 are fixed by connecting brackets 112, and the remaining adjacent truss beams 109 are fixed by connecting plates. The installation process of the steel wedge-shaped adjustment blocks 111 is as follows: 200T screw-type prefabricated wedge-shaped steel unloading blocks are used, with a maximum adjustment stroke of 10cm. After all the unloading blocks are brought to the site, a 400T hydraulic jack is used to make a reaction frame to verify the load-bearing capacity of the unloading blocks. The reaction pressure is 1.1 times the designed load-bearing capacity of 200T. After verification, a 25t truck crane and aerial work platform were used in conjunction with manual labor to install the blocks to the designed position. After the unloading blocks were installed, the elevation was checked again. The elevation was finely adjusted by adjusting the tie rods of the unloading blocks, and the elevation error was controlled within 2mm.

[0034] S8. Install the bottom formwork system 113 for casting the cap beam along the installed truss beam 109; S9. Steel reinforcement structural components used inside the cap beam, formed by steel bars; S10. The cap beam 114 is formed by secondary casting, creating an inverted T-shaped cap beam. The inverted T-shaped cap beam is formed by secondary casting, with the rectangular portion cast in one stage. The side and end formwork of the cap beam is made of Q235 steel, the panel is made of 6mm steel plate, the horizontal ribs are made of 10# channel steel @300mm, the vertical ribs are made of double-jointed (back-to-back) 20# channel steel @1000mm, and the tie rods are made of 25mm diameter threaded rods. Once the prestressing tensioning and grouting of the cap beam structure are completed and meet the design drawings or specifications, the truss beam 109 can be dismantled. S11, truss beam 109 removal: First remove the bottom formwork system 113, then remove the truss beam 109, and finally remove the clamp platform 102.

[0035] The further effects of the above construction method are: 1) Minimal impact on the existing structure: The truss beam structure has strong load-bearing capacity, high stiffness, and high stability, and can span the existing bridge structure in one span (maximum calculated span of 32.91m). Only 6 truss beams are needed to meet the load-bearing requirements of the cap beam structure with a self-weight of 1250 tons. 2) Excellent formability of the cap beam structure: Under the condition of a cap beam formwork with a maximum calculated span of 32.91m, 6 trusses, and a self-weight of 1250 tons, the maximum calculated deflection is only 47.3mm, far less than the requirement of L / 400 (L is the calculated span, which is 32.91m, with an allowable maximum deflection of 82.28mm) in the specification. The truss beam fabrication takes into account the pre-camber of 47.3mm to offset the construction deflection. Using steel wedge-shaped unloading blocks and a column-supported ground-mounted cap beam formwork platform, the formwork system exhibits almost no non-elastic deformation after the cap beam structure is constructed, allowing it to be formed according to the design drawings. 3) Outstanding economic and environmental benefits: Since the load-bearing platform fully utilizes the bearing capacity of the permanent structure, there is no need for large-scale foundation treatment and no solid waste is generated, resulting in significant environmental benefits; The "hybrid solid web member variable cross section truss beam" fully utilizes the high shear resistance of solid web members at various locations and the high bending resistance of truss beams. Compared with a fully solid web structure beam, the self-weight of this invention is about 45.5% lighter under the same working conditions.

[0036] The above construction method is applied to the construction of cap beams on old bridges with large spans, generally over 30 meters, for use on new viaducts. Because the existing old bridge deck is composed of precast box girders arranged piece by piece, several box girders will be removed from the center of the existing old bridge deck before the above construction method to meet the construction area of ​​the load-bearing column 101. Steps S1 to S8 in the above construction method are single-sided construction on the old bridge. In particular, the assembly jig 110 in step S6 is constructed and spliced ​​on the old bridge. This ensures that the construction of the new cap beam is carried out without affecting the traffic on the existing old bridge, greatly improving the construction progress.

[0037] In step S1, the pile head of the cast-in-place pile is removed to the designed pile top elevation using a pneumatic pick. If the concrete quality within the pile body area at the pile top elevation is poor, the removal continues down to the fresh concrete surface. A 2.8m diameter C40 concrete 118 is poured within 50cm of the bottom of the cast-in-place pile, and an HRB400 Φ25 reinforced concrete structure 115 is installed on the top surface. The pile perimeter is backfilled with slag with a thickness of not less than 1.0m in layers 119, with each layer less than 50cm thick and compacted with a road roller. After leveling the top of the slag with fine slag, a C30 HRB400 Φ16 reinforced concrete cushion layer is poured. After the cushion layer is poured, it is covered with geotextile for curing. The perimeter of the pile is 6.6m long and 4.8m wide along the direction of the reinforced concrete structure.

[0038] In step S3, the external prestressing system 103 is arranged in a relatively distributed manner along the length of the clamping platform and along the direction of the reinforcing bar structure 115. The external prestressing system 103 is composed of supporting timber 103-1, I-beams 103-2, and threaded steel 103-3. The supporting timber 103-1 is fixed on the clamping platform placement layer 100 and located on the outside of the clamping platform 102. The elevation of the supporting timber 103-1 is the same as the design bottom elevation of the lowest layer of steel web of the clamping platform 102. The elevation of the uppermost layer is adjusted using wedge blocks, and then I-beams 103-2 are installed sequentially. Each layer is spot-welded to the lower layer of I-beams 103-2. The distribution of the I-beams 103-2 is such that their webs are arranged sequentially from bottom to top, with the top and bottom plates stacked. Threaded steel bars 103-3 are inserted between adjacent I-beams 103-2, and the exposed lengths at both ends are adjusted to be consistent and the threaded steel bars 103-3 are tightened. The threaded steel bars 103-3 are located on both sides of the width direction of the clamping platform 102.

[0039] In step S5, each side of the supporting steel pipe group 105 consists of five supporting steel pipes 105-1. Adjacent supporting steel pipes 105-1 are connected by structural steel 105-2. Four of the supporting steel pipes 105-1 are symmetrically distributed along the center of the clamp platform 102 and close to the load-bearing column 101. The two supporting steel pipes 105-1 on one side of the load-bearing column 101 are connected and fixed to the connecting clamp 104 on the load-bearing column 101 by three structural steel 105-2. The other supporting steel pipe 105-1 is located on the outermost side and forms a triangular distribution at the center point between the two supporting steel pipes 105-1. The height difference between this supporting steel pipe 105-1 and the height of the other four supporting steel pipes 105-1 is the height of the longitudinal distribution beam 106. All the above connections are made by welding, with single-sided full fillet welds at the joints, and the weld leg height hf ≥ 4mm.

[0040] As attached Figure 7 , 13As shown, the truss beam 109 in steps S6 and S7 is a mixed solid-web variable cross-section truss beam, including two variable cross-section beams 1 and several adjustable truss beams 2. The adjustable truss beams 2 are rectangular cross-section beams. The several adjustable truss beams 2 are arranged in a straight line and fixed to each other to form a truss 3. The two variable cross-section beams 1 are located on both sides of the truss 3 and fixed. The variable cross-section beams 1 are fixed to the columns. The truss 3 spans across the top of the old bridge. Adjacent trusses 3 are connected and fixed by connecting frames 112. Compared with traditional truss beams, such as prefabricated Bailey beams or large-size steel structure main beams, which suffer from insufficient load-bearing capacity, the hybrid solid-web variable cross-section truss beams exhibit more uniform stress distribution. The main stress point is not concentrated on the load-bearing column 101. Through two variable cross-section beams 1, a portion of the corresponding stress points can be transferred to several adjusting truss beams 2. Since the bottoms of these adjusting truss beams 2 protrude from the variable cross-section beams 1 and transition through the lower sloping surface of the supporting beam 12, bending does not occur under the load-bearing requirements of a cap beam structure weighing thousands of tons.

[0041] As attached Figure 13 As shown, the variable cross-section beam 1 includes a solid web member beam 11 and a supporting member beam 12. The supporting member beam 12 and the solid web member beam 11 are connected and fixed by welding. The solid web member beam 12 is fixed on the load-bearing column 101. The supporting member beam 12 and the adjusting truss beam 2 are connected and fixed by bolt assembly, and the cross-section of the supporting member beam 12 is the same as the cross-section of the adjusting truss beam 2.

[0042] As attached Figure 14 As shown, the adjusting truss beam 2 includes an upper truss 21 and a lower truss 22, which are symmetrically distributed. Both ends of the upper truss 21 and lower truss 22 are provided with adjusting bolt holes 23. Three vertical web members 24 and two diagonal web members 25 are installed between the upper truss 21 and lower truss 22 at equal intervals. The two diagonal web members 25 are located between the three vertical web members 24 and are arranged in a "∧" shape. The junctions between the diagonal web members 25 and the vertical web members 24 are fixed by a connecting plate 26. The connecting plate 26 is fixed to the lower end face of the upper chord 21 or the upper end face of the lower chord 22. The web members are connected to the upper and lower chords and the connecting plate by welding. According to the length requirements of the mixed solid web variable cross-section truss beam on the actual site, the upper and lower chords can be made to a fixed size during the material cutting process, and then spliced ​​after forming. By adjusting the bolt holes 23, the length of the mixed solid web variable cross-section truss beam can be adjusted. It is suitable for various length changes and combinations, so as to be flexibly applied to project construction.

[0043] The bottom formwork system 113 in step S8 includes a crossbeam 113-1 and longitudinal beams 113-2. The crossbeam 113-1 is sequentially spliced ​​along the length of the truss beam 109. Two longitudinal beams 113-2 are installed on the crossbeam 113-1 along the length of the truss beam 109. The two longitudinal beams 113-2 are located on both sides of the load-bearing column 101. The crossbeam 113-1, which is sequentially spliced ​​along the length of the truss beam 109, is installed on the two longitudinal beams 113-2. Square timber 113-3 and bamboo plywood 113-4 are laid on the crossbeam 113-1. Because the cap beam structure has a particularly large load and the width of the cap beam exceeds 4.6m, when the transverse distribution beam is calculated as a simply supported beam structure, the rotation angle of the support point under load results in the outer two truss pieces having less or no force. To ensure uniform stress on the truss, a "secondary distribution beam" structure, that is, the setting of two crossbeams, is adopted.

[0044] In step S11, first remove the bottom formwork system 113, that is, adjust the steel wedge-shaped adjusting block 111 to symmetrically lower the beam by 5-10cm, and remove the square timber 113-3 and bamboo plywood 113-4. Then remove the horizontal beam 113-1 and the longitudinal beam 113-2 in sequence, and leave one horizontal beam 113-1 connected to the flower rack 112 as a spreader for dismantling the flower rack 112. Next, remove the truss beam 109, remove the connecting bolts between the flower rack 112 and the truss beam 109, and hang a section of the hand chain hoist on the horizontal beam 113-1. Use the hand chain hoist to lower the flower rack to the ground, and use a truck crane to lift the flower rack to the storage location. Remove the connecting flower rack 112 and the spreader of the transverse distribution beam piece by piece. The truss beam 109 outside the projection plane of the cap beam is removed by one truck crane and lifted to the ground jig for storage or transported to the next work surface for installation. The high-strength bolts of the truss beam girders are not removed.

[0045] In step S11, because the cap beam 114 has an inverted T-shaped structure, part of the truss beam 109 is located below the structural projection plane of the cap beam 114. Due to the limitations of the on-site working conditions, the truss beam 109 needs to be moved below the structural projection plane before being dismantled using a truck crane. The dismantling process is as follows: Install jack 116 onto the lower transverse distribution beam 107 of the truss beam 109, and adjust the top iron of jack 116 to be in close contact with the lower part of the truss beam 109. Use jack 116 to simultaneously lift the truss beam 109. Slowly lift the beam by about 3cm, install the translation trolley 117, and simultaneously and slowly reset the jack 116. The truss beam 109 will fall onto the translation trolley 117. Finally, remove the jack 116 and move the truss beam 109 to outside the projection plane of the cap beam 114. Use a truck crane to dismantle it, and the operation is the same as the dismantling method of the truss beam 109 outside the projection plane of the cap beam 114. Finally, remove the clamp platform 102, and dismantle the supporting steel pipe group 105 in order from top to bottom, and then remove the clamp platform 102.

[0046] The above are merely specific embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for cast-in-place construction of ultra-large span hybrid inverted T-shaped cap beams with truss-type supports, characterized in that: The construction method includes the following steps: S1. Construction of the load-bearing formwork foundation: pour a concrete cushion layer within the pile body of the cast-in-place pile and use it as a hoop platform (100), and cast the pile into a load-bearing column (101) that serves as a super-large span mixed inverted T-shaped cap beam. S2. Install a clamp platform (102) on the column body of the load-bearing column (101), and place the clamp platform (102) on the concrete pad. S3. Install an external prestressing system (103) on both sides of the clamping platform (102). S4. Installation of connecting clamps (104): Install one connecting clamp (104) every three meters along the height direction of the load-bearing column (101). S5. Support steel pipe assemblies (105) are installed on both sides of the clamp platform (102). A longitudinal distribution beam (106) and a transverse distribution beam (107) are installed above the support steel pipe assembly (105). A limit stop (108) is installed on the outer side of the transverse distribution beam (107), and the transverse distribution beam (107) extends out of the outer side of the support steel pipe assembly (105). S6. Truss beam (109) installation: The truss beam assembly frame is used to assemble the beams on the ground. The assembly frame (110) is equipped with two truss beams (109) for temporary fixing of the end segments. The truss beams (109) are configured and adjusted according to the overall length of the truss beams (109) required on site and spliced ​​with the two end segments of the truss beams (109) to form the beams. S7. Two truck cranes are used to place the spliced ​​truss beam (109) on the transverse distribution beam (107). Steel wedge-shaped adjustment blocks (111) are installed between the transverse distribution beam (107) and the truss beam (109). They are installed sequentially from the inner side to the outer side of the two opposite sides of the load-bearing column (101). The two truss beams (109) located on the inner side of the load-bearing column (101) are fixed by connecting brackets (112). The remaining adjacent truss beams (109) are fixed by connecting plates. S8. Install the bottom formwork system (113) for casting the cap beam along the installed truss beam (109). S9. Steel reinforcement structural components used inside the cap beam, formed by steel bars; S10. The cap beam (114) is formed by secondary casting and is cast into an inverted T-shaped cap beam; S11. Removal of truss beam (109): First, remove the bottom formwork system (113), then remove the truss beam (109), and finally remove the clamp platform (102).

2. The method for cast-in-place construction of ultra-large span hybrid inverted T-shaped cap beam truss support according to claim 1, characterized in that: In step S1, the pile head of the cast-in-place pile is removed to the designed pile top elevation using a pneumatic pick. If the concrete quality within the pile body area at the pile top elevation is poor, the removal continues to the fresh concrete surface. 2.8m diameter C40 concrete (118) is poured within 50cm of the pile bottom. HRB400Φ25 reinforced concrete structure (115) is configured on the top surface. A layer of slag with a thickness of not less than 1.0m (119) is used for backfilling around the pile. The layer thickness is less than 50cm and compacted by a road roller. After leveling the top of the slag with fine slag, a C30HRB400Φ16 reinforced concrete cushion layer is poured. After the cushion layer is poured, geotextile is covered for curing. The area around the pile is 6.6m long and 4.8m wide along the direction of the reinforced concrete structure.

3. The method for cast-in-place construction of ultra-large span hybrid inverted T-shaped cap beam truss support according to claim 1, characterized in that: In step S3, the external prestressing system (103) is arranged in a relatively distributed manner along the length of the clamping platform and along the direction of the reinforcing bar structure (115). The external prestressing system (103) is composed of supporting timber (103-1), I-beams (103-2), and threaded steel (103-3). The supporting timber (103-1) is fixed on the clamping platform placement layer (100) and located on the outside of the clamping platform (102). The elevation of the supporting timber (103-1) is the same as the design bottom elevation of the lowest layer of steel web of the clamping platform (102). Similarly, wedge blocks are used to adjust the elevation of the uppermost layer, and then I-beams (103-2) are installed in sequence. Each layer is spot-welded to the lower I-beam (103-2) for fixation. The distribution of the I-beams (103-2) is such that the web plates are arranged sequentially from bottom to top, and the top and bottom plates are stacked. Threaded steel bars (103-3) are inserted between adjacent I-beams (103-2), and the exposed lengths at both ends are adjusted to be consistent and the threaded steel bars (103-3) are tightened. The threaded steel bars (103-3) are located on both sides of the width direction of the clamping platform (102).

4. The method for cast-in-place construction of ultra-large span hybrid inverted T-shaped cap beam truss support according to claim 1, characterized in that: In step S5, there are five supporting steel pipes (105-1) on each side of the supporting steel pipe group (105). Adjacent supporting steel pipes (105-1) are connected by steel sections (105-2). Four of the supporting steel pipes (105-1) are symmetrically distributed along the center of the clamp platform (102) and close to the load-bearing column (101). The two supporting steel pipes (105-1) on one side of the load-bearing column (101) are connected and fixed to the connecting clamp (104) on the load-bearing column (101) by three steel sections (105-2). The other supporting steel pipe (105-1) is located on the outermost side and forms a triangular distribution at the center point between the two supporting steel pipes (105-1). The difference between the height of this supporting steel pipe (105-1) and the height of the other four supporting steel pipes (105-1) is the height of the longitudinal distribution beam (106).

5. The method for cast-in-place construction of ultra-large span hybrid inverted T-shaped cap beam truss support according to claim 1, characterized in that: The truss beam (109) in steps S6 and S7 is a mixed solid web variable cross section truss beam, including two variable cross section beams (1) and several adjustable truss beams (2). The adjustable truss beams (2) are rectangular cross section beams. The several adjustable truss beams (2) are arranged in a straight line and fixed to each other to form a truss (3). The two variable cross section beams (1) are located on both sides of the truss (3) and fixed. The variable cross section beams (1) are fixed on the columns. The truss (3) spans across the top of the old bridge. The adjacent trusses (3) are connected and fixed by connecting flower racks (112).

6. The method for cast-in-place construction of ultra-large span hybrid inverted T-shaped cap beam truss support according to claim 5, characterized in that: The variable cross-section beam (1) includes a solid web member beam (11) and a support member beam (12). The support member beam (12) and the solid web member beam (11) are connected and fixed by welding. The solid web member beam (12) is fixed on the load-bearing column (101). The support member beam (12) and the adjusting truss beam (2) are connected and fixed by bolt assembly. The cross-section of the support member beam (12) is consistent with the cross-section of the adjusting truss beam (2).

7. The method for cast-in-place construction of ultra-large span hybrid inverted T-shaped cap beam truss support according to claim 5, characterized in that: The adjustable truss beam (2) includes an upper truss (21) and a lower truss (22). The upper truss (21) and the lower truss (22) are symmetrically distributed, and both ends of the upper truss (21) and the lower truss (22) are provided with adjusting bolt holes (23). Three vertical web members (24) and two diagonal web members (25) are installed between the upper truss (21) and the lower truss (22). The two diagonal web members (25) are located between the three vertical web members (24) and are distributed in a "∧" shape. The intersection point between the diagonal web members (25) and the vertical web members (24) is fixedly connected by a gusset plate (26). The gusset plate (26) is fixed on the lower end face of the upper truss (21) or the upper end face of the lower truss (22).

8. The method for cast-in-place construction of ultra-large span hybrid inverted T-shaped cap beam truss support according to claim 1, characterized in that: The bottom formwork system (113) in step S8 includes a crossbeam (113-1) and a longitudinal beam (113-2). The crossbeam (113-1) is formed by splicing together along the length of the truss beam (109). Two longitudinal beams (113-2) are installed on the crossbeam (113-1) along the length of the truss beam (109). The two longitudinal beams (113-2) are located on both sides of the load-bearing column (101). The crossbeam (113-1) is formed by splicing together along the length of the truss beam (109) on the two longitudinal beams (113-2). Square timber (113-3) and bamboo plywood (113-4) are laid on the crossbeam (113-1).

9. The method for cast-in-place construction of ultra-large span hybrid inverted T-shaped cap beam truss support according to claim 8, characterized in that: In step S11, first dismantle the bottom formwork system (113), that is, adjust the steel wedge-shaped adjusting block (111) to symmetrically lower the beam by 5-10cm, and remove the square timber (113-3) and bamboo plywood (113-4). Then, remove the horizontal beam (113-1) and the longitudinal beam (113-2) in sequence, and leave one horizontal beam (113-1) on the connecting flower rack (112) intact, as a carrying pole for dismantling the connecting flower rack (112); then remove the truss beam (109), and remove the connecting beam. Connect the connecting bolts between the flower rack (112) and the truss beam (109), and hang a section of the hand chain hoist on the crossbeam (113-1). Use the hand chain hoist to gradually lower the flower rack to the ground, and use a truck crane to lift the flower rack to the storage location. Remove the connecting flower rack (112) and the horizontal distribution beam spreader piece by piece. Use a truck crane to remove the truss beam (109) outside the projection plane of the cap beam, and lift it to the ground jig for storage or transfer it to the next work surface for installation. Do not remove the high-strength bolts of the truss beam girders.

10. The method for cast-in-place construction of ultra-large span hybrid inverted T-shaped cap beam truss support according to claim 1, characterized in that: In step S11, because the cap beam (114) is an inverted T-shaped structure, some truss beams (109) are located below the structural projection plane of the cap beam (114). Due to the limitations of the on-site operation conditions, the truss beams (109) need to be moved below the structural projection plane before being dismantled by a truck crane when the load-bearing structure is demolished. The demolition process is as follows: Install jacks (116) onto the lower transverse distribution beams (107) of the truss beams (109), and adjust the top iron of the jacks (116) to be in close contact with the lower part of the truss beams (109). Use jacks (116) to synchronously and slowly lower the truss beams (109). Slowly lift the jack by about 3cm, install the translation trolley (117), and simultaneously and slowly reset the jack (116). The truss beam (109) falls onto the translation trolley (117). Finally, remove the jack (116), and move the truss beam (109) to outside the projection plane of the cap beam (114). Use a truck crane to remove it. The operation is the same as the removal method of the truss beam (109) outside the projection plane of the cap beam (114). Finally, remove the clamp platform (102), and remove the supporting steel pipe group (105) in order from top to bottom. Remove the clamp platform (102).

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