Two-stage construction method for lower cross beam of cable tower of cable-stayed bridge

Abstract

The invention relates to a two-stage construction method for a lower cross beam of a cable-stayed bridge tower. The two-stage construction method comprises the steps that S1, a tower base and a tower body root are constructed; s2, a tower column is poured along the root of the tower body, and a support segment spliced with the lower cross beam is not poured firstly; s3, a lower cross beam support is installed between the two tower columns; s4, setting steel molds are arranged in the areas where the support segments are located, and sand molds are backfilled; s5, lower cross beam concrete pouring is conducted, a first-stage steel beam tensioning hole channel and a second-stage steel beam tensioning hole channel are reserved, a lower cross beam formwork system is dismantled before tensioning, and only a bottom formwork is reserved; s6, the sand mold is removed, and the shaping steel mold is dismantled; s7, a support section steel reinforcement framework is bound, then a formwork is erected to pour a support section, the support section and the lower cross beam are poured into a whole, a steel beam tensioning hole channel reserved in the support section communicates with a second-stage steel beam tensioning hole channel of the lower cross beam, and a formwork is removed before tensioning; and S8, dismounting the lower cross beam bracket. The problem that a mass concrete beam-column joint is prone to cracking can be solved.

Description

TECHNICAL FIELD

[0001] The present application relates to a bridge construction method, in particular to a two-stage construction method for the lower beam of a cable-stayed bridge tower. BACKGROUND

[0002] As disclosed in Chinese patent application publication CN 110886227 A, a main tower cast-in-place lower beam support system and construction method are disclosed, wherein the first layer of concrete of the lower beam is poured and maintained: after the installation of the lower beam bottom formwork, outer formwork and inner formwork is completed, the tower column and the lower beam are synchronously poured with concrete and the concrete is maintained. When the tower column and the lower beam are synchronously poured with concrete, due to the shrinkage of the mass concrete, the connecting node of the tower column and the lower beam is in tension, and the tensile strength of the concrete is low, which easily causes excessive cracks at the node and affects the construction quality. SUMMARY

[0003] The purpose of the present application is to provide a two-stage construction method for the lower beam of a cable-stayed bridge tower, which separately constructs the lower beam on the support, and after the mass concrete pouring of the lower beam is completed, the first-stage steel strand is tensioned to apply pre-compressive force. At this time, the two ends of the lower beam are in compression, and the compressive deformation of the lower beam has been completed. Subsequently, the tower column is integrally poured, avoiding excessive deformation of the mass concrete beam-column node due to the pre-stress tensioning of the lower beam, which causes cracking at the tower column node.

[0004] To achieve the above-mentioned purpose, a two-stage construction method for the lower beam of a cable-stayed bridge tower is adopted, which comprises the following steps: S1: constructing the tower base and the tower body root of the tower column located on the tower base; S2: pouring the tower column along the tower body root, without pouring the support segment spliced with the lower beam, the pouring of the support segment is delayed until the construction of the lower beam is completed; S3: installing the lower beam support on the two tower columns, installing the lower beam formwork system on the lower beam support, and binding the steel reinforcement framework in the intersection area of the lower beam and the support segment; S4: setting a shaped steel form in the area where the support segment is located, the top surface of the shaped steel form is spliced with the bottom form of the formwork system, and the shaped steel form encloses an area filled with sand mold pads on the bottom surface of the cantilevered end of the poured lower beam, as well as the bottom surface of the end form and the side form of the lower beam formwork system; S5: the lower beam is constructed using the post-tensioned prestressed concrete construction technology, the lower beam is provided with first-stage steel strand tensioning ducts and second-stage steel strand tensioning ducts, the steel strand inserted in the first-stage steel strand tensioning ducts is tensioned after the pouring of the concrete of the lower beam is completed, and when the actual strength of the concrete increases to a percentage preset value of the design value, the formwork system of the lower beam is removed before tensioning, only the bottom form is retained, and the ducts are grouted after tensioning is completed; S6: remove the sand mold, and remove the shaped steel mold in the area where the support segment is located, and completely convert the lower beam concrete load into lower beam support support; S7: bind the remaining steel framework of the support segment, and then erect the mold to pour the support segment, and the support segment is poured as a whole with the lower beam, the reserved steel beam tension channel on the support segment is communicated with the second stage steel beam tension channel of the lower beam; when the actual strength of the concrete increases to a percentage preset value of the design value, tension is carried out again, the formwork is removed before tension, and the channel is grouted after tension is completed; S8: remove the lower beam support.

[0005] In this way, the lower beam is constructed in advance, the shrinkage deformation of the lower beam mass concrete is completed in advance, the lower beam is tensioned in advance, the two ends are compressed in advance, and the internal tension of the node due to the shrinkage of the concrete is avoided after the node is poured at the same time. The backfilling sand mold can improve the bearing capacity of the sand mold through lateral constraint of the shaped steel mold and the hoop effect, compared with pouring a section of the tower column to support the tower column node concrete to be poured in sections, thereby increasing the construction joint of the beam-column node, and the backfilling sand mold and the shaped steel mold can replace the backfilling sand mold, which can be unloaded and removed subsequently, facilitate one-time pouring of the tower column beam-column node position, and reduce the construction joint of the beam-column node.

[0006] As a further improvement of the application, the tower column is a broken line inclined type, which is poured in a segmented manner, with the next segment supporting the previous segment, the support segment expanding outward below, and the support segment inward above, and there are two segments between the support segment and the tower body root.

[0007] In this way, the support segment can adapt to the span of the lower beam, and the overall barycenter can be inwardly retracted above the support segment.

[0008] As a further improvement of the application, the steel reinforcement framework of the lower beam is provided with anchoring steel bars at both ends extending into the area to be poured with the support segment.

[0009] As a further improvement of the application, the first stage prestress tensioning uses ordinary anchors, and the second stage prestress tensioning uses deep-embedded anchors, and the support segment is provided with an anchoring sealing groove outside to pour an anchoring concrete plate to connect the deep-embedded anchors.

[0010] In this way, the ordinary anchors are beneficial to the stress of the lower beam bottom tension area, the local compression facilitates the arch, the deep-embedded anchors need the concrete anchoring plate to disperse the stress, and the tower column side wall is beneficial to the overall compression and uniform stress.

[0011] As a further improvement of the application, the sand mold is filled with sand pads, and the top surface of the sand layer is leveled with cement mortar.

[0012] As a further improvement of the present application, the first-stage steel beam tensioning hole is arranged in the core area of the bottom of the lower cross beam to tension the arch; the second-stage steel beam tensioning hole is arranged in the edge area of the bottom of the lower cross beam and the upper area of the lower cross beam.

[0013] In this way, the lower cross beam is tensioned alone, and the lower cross beam is fully deformed alone; and the concrete tensile stress at the position of the subsequent two-end beam-column joint is reduced.

[0014] As a further improvement of the present application, in the first-stage prestress tensioning and the second-stage prestress tensioning, the tensioning control adopts tensioning force and elongation value double control, and stress control is mainly used, and elongation value is used for checking; In the first stage, after the concrete reaches 95% of the design strength, a total of 16 prestressed steel beams are tensioned and anchored at the end of the lower cross beam interface; in the second stage, a total of 72 prestressed steel beams are tensioned and anchored on the outer wall of the tower column; all the prestressed steel beams adopt circular metal bellows hole forming.

[0015] As a further improvement of the present application, the sand filling adopts backfilling medium sand with a particle size of 0.075-4.75 mm, and the water content of the sand is not more than 5%, and the clay content is not more than 2%; during backfilling, the sand should be layered and tamped, and the single backfilling thickness is not more than 30 cm; during tamping, the sand is tamped by watering; after the sand is backfilled to a distance of 20 cm from the lower chamfer of the lower cross beam, the bearing capacity is tested, and the bearing capacity is not less than 180 kPa; finally, 20 cm thick cement mortar leveling is carried out, and the part of the lower cross beam overhanging the bottom mold is padded.

[0016] As a further improvement of the present application, the lower cross beam support is pre-pressed after installation, and the pre-pressing material adopts 1×1×0.9 m concrete precast block, and the weight of a single precast block is 2.2 t, and the zero number is supplemented by sand bags, and the pre-pressing is divided into three levels of 60%, 100%, and 120% for pre-pressing observation, and the deformation observation and statistical analysis are carried out during the pre-pressing process, and the specific steps are as follows: A1: First-stage loading 60% pre-pressing block distribution The pre-pressing block is 1×1×0.9 m unit weight 2.2 t, and a total of 390 blocks are arranged in three layers, 160 blocks are arranged in the first layer, 160 blocks are arranged in the second layer, and 70 blocks are arranged in the third layer, and the remaining 3.90 t is supplemented by 20 unit weight 0.2 t sand bags; A2: Second-stage loading 100% pre-pressing block distribution The pre-pressing block is 1×1×0.9 m unit weight 2.2 t, and a total of 650 blocks are arranged in five layers, 160 blocks are arranged in the first layer, 160 blocks are arranged in the second layer, 160 blocks are arranged in the third layer, 160 blocks are arranged in the fourth layer, and 10 blocks are arranged in the fifth layer, and the remaining 6.50 t is supplemented by 33 unit weight 0.2 t sand bags; A3: The pre-compression blocks are 1×1×0.9m with a unit weight of 2.2t. A total of 780 pre-compression blocks are arranged in 5 layers. 160 blocks are arranged in the 1st layer, 160 blocks in the 2nd layer, 160 blocks in the 3rd layer, 160 blocks in the 4th layer, and 140 blocks in the 5th layer. The remaining 7.80t is supplemented by 39 heavy sandbags with a unit weight of 0.2t. A4: After preloading to 120%, observe every 6 hours. The principle for preloading unloading time is that the deformation of the lower beam support is stable. When the difference between the average values ​​of the last two settlement observations is not greater than 2mm, preloading is terminated and unloading is carried out. The unloading order is the reverse of the weight and observation records are made. After all the weights are unloaded, the measurement data of the bracket is statistically analyzed. Unloading should be carried out according to the principles of symmetry, layering, and grading. The first stage should be unloaded to 100% of the design value; the second stage should be unloaded to 60% of the design value; and the last stage should be unloaded completely. After each stage of unloading, the unloading should be stopped for 1 hour and observed. Then, unloading should continue. Based on the measured linear and inelastic deformation, the elevation of the vertical formwork should be determined, and the elevation of the bottom formwork can be adjusted.

[0017] As a further improvement of the present invention, the data of the bottom formwork observation points should be measured and recorded before loading, as the initial data values ​​for preloading settlement observation; After each loading, stop for 1 hour to measure the vertical and lateral deformation values. Then, monitor and record the displacement of each observation point at 6-hour intervals. Loading can only proceed if the difference between the average displacement of two consecutive monitoring measurements is no greater than 2mm. After loading to 120%, monitor and record the displacement of each observation point at 6-hour intervals. Settlement can be considered to be stable and unloading can begin when the difference between the average displacement of 12 consecutive hours is no greater than 2mm. The displacement of each monitoring point should be measured and recorded 6 hours after the support is unloaded. During the loading process, the measurement team should use instruments to observe the deformation and sinking of the support. The specific observations should be based on actual observations. If the deformation and sinking rate is found to be significantly accelerated, the preloading should be stopped immediately, the workers should be evacuated, and the plan should be modified and the support reinforced.

[0018] The beneficial effects of this invention are as follows: (1) First, construct the lower crossbeam separately on the support. After the large volume of concrete of the lower crossbeam shrinks, apply preload by tensioning. At this time, both ends of the lower crossbeam are under pressure. Then, pour the concrete into the tower column as a whole to avoid cracking and damage at the joint due to the shrinkage of the concrete volume.

[0019] (2) By setting up a "sand mold" section, the steel reinforcement cage in the intersection area of ​​the lower crossbeam and the tower column support section is tied before the lower crossbeam is poured. The steel reinforcement can undergo slight deformation in the sand mold, thereby adapting to the compression deformation of the lower crossbeam and avoiding cracking of the concrete at the edge of the tower column. Attached Figure Description

[0020] Figure 1The construction diagram of tower base and 1m high tower body adjustment section.

[0021] Figure 2 The construction diagram of pouring the lower tower column twice to 2m below the lower cross beam.

[0022] Figure 3 The construction diagram of tower column to 9.6m, installation of lower cross beam support.

[0023] Figure 4 The construction diagram of lower cross beam support on both sides of the tower column, arrangement of formwork and sand filling in the form.

[0024] Figure 5 The construction diagram of prestressed concrete lower cross beam by post-tensioning method, completion of the first prestressed tendon tensioning.

[0025] Figure 6 The construction diagram of sand filling and removal.

[0026] Figure 7 The construction diagram of lower cross beam on both sides of the tower column, and completion of the second prestressed tendon tensioning.

[0027] Figure 8 The construction diagram of lower cross beam support removal.

[0028] Figure 9 The construction diagram of lower cross beam support elevation.

[0029] Figure 10 The construction diagram of Figure 9 A-A section in the middle.

[0030] Figure 11 The construction diagram of Figure 9 B-B section in the middle.

[0031] Figure 12 The construction diagram of tower base top embedded steel plate + anchor reinforcement structure.

[0032] Figure 13 The construction diagram of Figure 12 Embedded steel plate plan view in the middle.

[0033] Figure 14 The construction diagram of Figure 12 Anchor reinforcement full filling welding detail view in the middle.

[0034] Figure 15 The construction diagram of lower cross beam support steel pipe column foot stiffener plate welding.

[0035] Figure 16 The construction diagram of Figure 15 Column foot plan view in the middle.

[0036] Figure 17 The construction diagram of Figure 15 Stiffener plate size view in the middle.

[0037] Figure 18 Setting drawing for example 268# pier body bracket.

[0038] Figure 19 Setting drawing for example 269# pier body bracket.

[0039] Figure 20 Elevation view of bracket climbing cone.

[0040] Figure 21 Plan view of bracket climbing cone.

[0041] Figure 22 Table of climbing cone components.

[0042] Figure 23 Fixing diagram of side formwork.

[0043] Figure 24 Plan view of example 268# pier lower beam support.

[0044] Figure 25 Plan view of example 269# pier lower beam support.

[0045] Figure 26 Diagram of sand cylinder.

[0046] Figure 27 Detail drawing of example 268# pier body bracket column.

[0047] Figure 28 Elevation view of example 268# pier lower beam support preloading block 60% preloading arrangement.

[0048] Figure 29 Side view of example 268# pier lower beam support preloading block 60% preloading arrangement.

[0049] Figure 30 Elevation view of example 269# pier lower beam support preloading block 60% preloading arrangement.

[0050] Figure 31 Side view of example 269# pier lower beam support preloading block 60% preloading arrangement.

[0051] Figure 32 Elevation view of example 268# pier lower beam support preloading block 100% preloading arrangement.

[0052] Figure 33 Side view of example 268# pier lower beam support preloading block 100% preloading arrangement.

[0053] Figure 34 Elevation view of example 269# pier lower beam support preloading block 100% preloading arrangement.

[0054] Figure 35 Figure 17 is a side view of the pre-stressed block arrangement for the example 269 # pier beam support pre-stressed block 100% pre-stressed.

[0055] Figure 36 Figure 18 is an elevation view of the pre-stressed block arrangement for the example 268 # pier beam support pre-stressed block 120% pre-stressed.

[0056] Figure 37 Figure 19 is a side view of the pre-stressed block arrangement for the example 268 # pier beam support pre-stressed block 120% pre-stressed.

[0057] Figure 38 Figure 20 is an elevation view of the pre-stressed block arrangement for the example 269 # pier beam support pre-stressed block 120% pre-stressed.

[0058] Figure 39 Figure 21 is a side view of the pre-stressed block arrangement for the example 269 # pier beam support pre-stressed block 120% pre-stressed.

[0059] Figure 40 Figure 22 is an elevation view of the observation point arrangement for the example 268 # pier beam support.

[0060] Figure 41 Figure 23 is a plan view of the observation point arrangement for the example 268 # pier beam support.

[0061] Figure 42 Figure 24 is an elevation view of the observation point arrangement for the example 269 # pier beam support.

[0062] Figure 43 Figure 25 is a layout diagram of the settlement observation points for the example steel pipe pile foundation.

[0063] Figure 44 Figure 26 is a cross-sectional view of the lower beam pre-stressed tendon arrangement.

[0064] Figure 45 Figure 27 is a schematic diagram of the lower beam end surface pre-stressed tendon arrangement.

[0065] Figure 46 Figure 28 is a large sample diagram of the sealing anchor concrete.

[0066] Reference signs: 1, tower base; 2, tower column; 201, tower body root; 3, lower beam; 301, first stage steel tendon tensioning channel; 302, second stage steel tendon tensioning channel; 4, lower beam support; 5, formwork system; 501, bottom form; 6, sealing anchor concrete plate; 7, sand mold. DETAILED DESCRIPTION

[0067] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0068] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. The terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Furthermore, unless otherwise explicitly specified and limited, the terms "installed," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0069] Example 1 like Figures 1-46 As shown, the construction process of the lower tower column and lower crossbeam of the 268# main tower in this embodiment specifically includes the following steps: First step, such as Figure 1 As shown, the tower base 1 and the 1m high tower body root 201 are constructed together, with the tower body root serving as the tower body adjustment section; The second step, as Figure 2 As shown, the lower tower column was poured in two stages to a depth of 2m below the lower crossbeam 3 (9.6m high) using a fixed steel mold. The third step, as Figure 3 As shown, after the tower column is constructed to 9.6m, the lower crossbeam support 4 is installed; Step four, as Figure 4 As shown in section 4.1, formwork is installed and reinforced for the 9.6m to 11.6m section of the tower column; 4.2 Fill the area within the vertical mold with sand, moisten it with water, and smooth the top 10cm with mortar.

[0070] Fifth step, as Figure 5As shown in Figure 5.1, tie the reinforcing bars of the lower crossbeam (including the portion extending 89cm into the tower column), arrange the first post-tensioned prestressing tendons, and erect the formwork to pour concrete. (Note the pre-embedded prestressing tendons extending to the outside of the tower column.) 5.2 Once the concrete has reached the required age, strength, and modulus of elasticity as designed, the prestressing tendons in the lower crossbeam are tensioned and grouted. Step 6, as follows Figure 6 As shown in Figure 6.1, allow the material to stand for the appropriate time according to the design requirements; 6.2 Remove the sand filling within the 9.6m to 11.6m range of the tower column and clean it thoroughly; 6.3 When designing the lower crossbeam support, it is necessary to consider that the concrete load originally acting on the tower column will be transferred to the support. Step 7, as Figure 7 As shown in Figure 7.1, the steel bars within the range of 9.6m to 19.0m of the tower column are tied, and the prestressed tendons of the lower crossbeam are extended to the outside of the tower column. The formwork is then erected and concrete is poured.

[0071] 7.2 Once the concrete has reached the required age, strength, and modulus of elasticity as designed, the prestressing tendons extending to the outer side of the tower column are tensioned and grouted.

[0072] Step 8, as Figure 8 As shown, 8.1, dismantle the lower crossbeam support; 8.2, set up the climbing formwork system and carry out the construction of the middle tower column.

[0073] The lower crossbeam support adopts the form of steel pipe support. Steel pipes are installed by setting embedded parts on the top surface of the tower base as support, and longitudinal and transverse distribution beams are laid on top of it and placed under the bottom formwork 501.

[0074] like Figures 9-11 As shown, pier #268 uses a support system consisting of 3 rows and 3 columns of φ820×12mm steel pipe columns, plus 5 rows of pre-embedded corbels on each side of the pier. The main towers at both ends are lowered and backfilled with graded sand, serving as the load-bearing points for the end formwork. Double-layered I56b I-beam distribution beams are installed at the top of the steel pipe columns. φ630×10mm steel pipe columns and double-layered HM588 steel sections are installed on the corbels. Double-layered HM588 steel load-bearing beams are arranged on the top surface of the distribution beams at the column tops. These load-bearing beams are supported by the distribution beams at the column tops and the pre-embedded corbels on the inner side of the second section of the tower column. A bottom formwork system is laid on top of the load-bearing beams. Connecting systems are installed between the steel pipe columns, using φ325×8mm steel pipes. Both longitudinal and transverse connecting systems are welded to the steel pipe columns. Both the side formwork and the passageway use standardized steel formwork. The inner formwork is made of 1.5cm bamboo plywood and 10×10cm square timber, with the square timber arranged 20cm apart in the center. I10 I-beams are placed under the square timbers as distribution beams, and the I10 I-beams support the top of the steel pipe scaffolding. The inner formwork support system uses φ48*3.5mm steel pipe scaffolding, with a horizontal bridge spacing of 90cm, with local adjustments to the spacing. The longitudinal bridge spacing is 60cm, and the vertical step distance is 65cm.

[0075] 2. Bracket Installation 1) Pivot installation (1) Construction of steel pipe column embedded steel plate like Figures 12-14 As shown, during tower base construction, embedded parts are installed on its top surface. The embedded parts are steel plate + anchor bar structures. The embedded plate and the anchor bar are welded together by full-fill welding. The anchor bar is φ20mm threaded steel and penetrates 45cm into the foundation (tower base). The embedded steel plate is 20mm thick. Each embedded steel plate is arranged with two rings of anchor bars. The inner ring has 8 bars evenly distributed around a diameter of 700mm, and the outer ring has 12 bars evenly distributed around a diameter of 920mm.

[0076] like Figures 15-17 As shown, the column base of the steel pipe column is fully welded to the embedded parts in the circumferential direction, and eight stiffening plates are evenly welded along the outer wall of the steel pipe in the circumferential direction. The weld leg height is 8mm, and it is a third-level weld.

[0077] (2) Construction of the corbel embedded in the pier body like Figures 18-21 As shown, the load-bearing points on the pier are set using a combination of pre-embedded climbing cones and corbels. For pier #269, each pier column has 3 corbels along the longitudinal direction of the bridge, and for pier #268, each pier column has 5 corbels along the longitudinal direction of the bridge. Each corbel position requires the pre-embedding of 12 M42 climbing cones.

[0078] ① Requirements for pre-embedded climbing cone processing: A. Before processing, the quality of raw materials should be inspected, mainly checking whether the materials have a certificate of conformity from the manufacturer and whether there are any defects or rust on the appearance. In addition, since the embedded parts are load-bearing components, necessary mechanical property retesting and chemical composition analysis are required before use.

[0079] B. Materials and processing shall be carried out strictly in accordance with the dimensions and requirements of the construction drawings. High-strength screws shall be cut using a grinding wheel machine, and gas cutting shall be strictly prohibited.

[0080] C. For example Figure 22 As shown, first assemble the climbing cone, high-strength bolt, and embedded plate into a set; after applying grease to the hole of the climbing cone, tighten the high-strength bolt to ensure that concrete does not flow into the thread of the climbing cone; wrap the outside of the climbing cone with tape and grease for easy disassembly; then screw the embedded plate onto the other end of the high-strength bolt, with the cone facing the template and in the opposite direction to the climbing cone.

[0081] D. The anchor plate is made of thick steel plate and welded to the bracket. During welding, the flatness of the anchor plate is ensured, and water is sprayed to cool it down, preventing the anchor plate from twisting and deforming due to overheating during welding.

[0082] ② Installation and positioning: A. The embedded part is located on the side of the concrete. Due to the large size of the anchor plate and high installation accuracy, the embedded part system is fixed on the formwork with installation bolts or positioning bolts according to the construction drawings (see Figure 23 ); B. According to the construction drawings, the installation position of the embedded part is calculated, and the embedded part is laid out by total station and steel tape.

[0083] C. The embedded part should not be in contact with the main reinforcement, and should be set inside the main reinforcement; the embedded part should not protrude from the surface of the concrete, nor should it be larger than the shape of the member; the position deviation of the embedded part should meet the requirements.

[0084] D. After the installation of the embedded part system is completed, the soil cloth is used to block the climbing cone hole, and the transparent adhesive tape is used to wrap the end to prevent the cement slurry from entering the cone hole during pouring.

[0085] ③ Matters needing attention during concrete pouring: A. The concrete can be poured only after the formwork, reinforcement, embedded part, etc. are checked to be qualified. If displacement of the embedded part is found during concrete pouring, pouring should be stopped, the cause should be found out, and the embedded part should be properly fixed before the concrete initial setting.

[0086] B. During concrete pouring, the vibration rod should avoid direct contact with the embedded part, and should be careful near the embedded part. The position of the embedded part should be observed while vibrating, and the position of the embedded part should be corrected in time to ensure that it does not produce excessive displacement.

[0087] ④ Anchor plate installation A. After the concrete formwork is removed, the actual position of the climbing cone is re-measured, and the deviation from the position in the construction drawings is checked. If the deviation is large, the anchor plate hole should be opened according to the actual position to ensure effective connection between the anchor plate and the embedded part system and to ensure the overall stress requirements of the embedded part. If there is a small deviation between the installation position of the individual climbing cone and the position in the construction drawings, the anchor plate hole can be reamed, a certain thickness of pad plate is added, the pad plate is welded with the anchor plate, and a lengthened stress bolt is selected for fixation.

[0088] B. The stress bolts on the anchor plate are twisted and sheared with a wrench one by one until they are in place. When designing the bracket, the available construction space should be fully considered. If it is found that the embedded part system is installed with inclination, spring washers should be added to the stress bolts to prevent the stress bolts from loosening. The tightness of the bolts should be checked regularly during the construction process of the embedded part.

[0089] C. When the bracket is assembled and welded, measures should be taken to prevent the anchor plate from deforming and to ensure that the weld quality meets the specification requirements.

[0090] ⑤ Demolition After the embedded part is used, the stress bolts are removed one by one, the anchor plate is removed, and the climbing cone is taken out by reversing the screw with a special unloading tool. The surface of the stress bolt after being taken out is cleaned and oiled, and it is stored for circulation use. ⑥ Repair After the pre-embedded demolition is completed, the tape inside the climbing cone hole is chiseled out and wetted with water. A special concrete repair agent is used to seal the climbing cone hole. The color of the repair agent should be consistent with the color of the concrete to ensure that there is no color difference on the surface of the repaired climbing cone hole.

[0091] (3) Pier body backfilling sand construction 268# Pier column backfilling medium sand (particle size 0.075-4.75mm), the water content of the sand should not exceed 5%, and the clay content should not exceed 2%. When backfilling, it should be layered and compacted, and the single backfilling thickness should not exceed 30cm. During the compaction process, it should be compacted by sprinkling water. After backfilling to 20cm from the lower corner of the lower beam, the bearing capacity test must be carried out, and the bearing capacity must not be less than 180KPa. Finally, 20cm thick cement mortar leveling is carried out.

[0092] According to the weight of the 0.89cm long concrete of the overhanging part of the lower beam, it is 7.4*0.89*9.3*2.4=147t, and the 20cm mortar leveling surface transmits the concrete load according to the 45° angle, and the contact area is about 9.3*1m=9.3m 2 , so the foundation stress is 147*10 / 9.3=158KPa, so the backfill layer simulates the foundation, and its bearing capacity is controlled according to 180KPa to meet the requirements.

[0093] 2) Steel pipe column installation After the rust and dirt on the embedded plate are cleaned, the single steel pipe column is hoisted. Since the pile cap has not been completely backfilled at this time, the lifting equipment needs to be placed outside the cofferdam for hoisting, with the farthest hoisting distance being about 25m. The heaviest single steel pipe column is 2.63t, which can be lifted by a 50t crawler crane (working radius 26m, lifting arm length 30m, rated lifting 7.7t). Two-point lifting is adopted using φ24mm, 6*37M-FC-1770 type steel wire rope, and full circumferential welding is adopted with the embedded plate, with the weld leg height not less than 8mm, and stiffener welding along the circumference. The stiffener, the steel pipe column and the embedded plate are all circumferentially welded, with the weld leg height not less than 8mm. Before welding the steel pipe column, the verticality and plane position of the steel pipe column should be corrected using a total station. When the verticality and plane position meet the requirements, welding operation can be carried out.

[0094] The allowable deviation between the center of the steel pipe column and the center of the pile foundation is ±1cm; The verticality of the steel pipe column is 0.1% and not more than 2cm.

[0095] When the length of a single steel pipe column is not enough, butt joint full welding is adopted, and stiffener welding is carried out along the circumference of the steel pipe column. The stiffener is 10mm thick and 300*150mm in size, and is circumferentially welded with the steel pipe, with the weld leg height not less than 12mm.

[0096] The whole steel pipe column hoisting adopts steel wire rope φ24mm, 6×37M-FC-1770 type steel wire rope, adopts two-point hoisting, and the steel wire rope is almost perpendicular to the hoisted object, without considering the included angle.

[0097] The breaking force of the steel wire rope is 32.5t, and considering the uneven stress coefficient of the steel wire rope 0.82, the actual allowable breaking tension of a single steel wire rope is [P]=32.5×0.82=26.65t.

[0098] The heaviest single steel pipe is 2.63t, and each steel wire rope has one steel wire rope with a diameter of 24mm, so the safety factor of the steel wire rope is 26.65 / 1.315=20.2>8 times, which meets the requirements.

[0099] As shown in Figures 24-25 , after the steel pipe column is completely welded, the connection between the steel pipe columns is welded, and the connection is welded in the form of φ325×8mm steel pipe penetrating the column, the weld leg is 6mm, and the weld is three grades.

[0100] 3) Sand barrel installation The support system adopts sand barrel as the unloading device, which is arranged at the top of the steel pipe column. The sand barrel is made of a thick and thin steel pipe with a sealing plate. The lower thick steel pipe is filled with sand, and the upper thin steel pipe is filled with concrete and inserted into the thick steel pipe at the bottom as a piston to form a retractable device. After the pre-stressed engineering construction of the lower cross beam is completed and meets the design requirements, the support can be unloaded through the sand barrel.

[0101] The sand barrel is made of hot-rolled seamless steel pipe, and dry medium sand is filled inside. Two sand extraction holes are provided at the bottom of the barrel body and sealed with bolts; the piston barrel body is also made of hot-rolled seamless steel pipe and is inserted into the lower barrel body. See Figure 26 for details. The designed bearing capacity of the sand barrel is 201t, and a pre-test is required before use to obtain the corresponding settlement data as the basis for setting the settlement amount.

[0102] Sand barrel construction precautions: (1) After the barrel plug is processed, the periphery should be polished smooth and greased; (2) The sand filled in the lower barrel body should be sieved medium sand with good fluidity and mud content not greater than 2%, and the sand should be dried to ensure that the water content is not greater than 1%. After the above indicators are qualified, the sand can be loaded; (3) In order to ensure the uniform stress of the sand barrel top, the top surface of the sand barrel steel pad should be tightly filled with thin steel plate to tightly fit the beam bottom and the sand barrel top surface.

[0103] After the sand barrel is hoisted to the top of the column, it should be fixed firmly, and if necessary, it should be fixed by electric welding.

[0104] 4) Installation of distribution beam For pier #268, φ630×10mm steel pipe columns (with column caps) need to be welded to the corbels on the side of the pier body to adjust the elevation of the bottom formwork system. The bottom of the φ630×10mm steel pipe column should be fully welded to the contact surface of the sand cylinder, and the weld leg height should not be less than 8mm. Then, double HM588 steel distribution beams are hoisted on top, and temporary assemblies are welded on the double HM588 steel to adjust the angle of the bottom formwork support.

[0105] For the three rows of steel pipe columns in the middle of pier #268, double-span I56b I-beam distribution beams are hoisted above the sand cylinder and spot-welded to the sand cylinder. After the distribution beams are hoisted, double-span HM588 steel load-bearing beams are installed. There are five sets of these load-bearing beams, each set consisting of three sections: non-standard load-bearing beams on both sides of the arc section and standard load-bearing beams on the straight section. Due to the long overall length, each set is cut in the middle and hoisted into place in two stages. The beams are then welded together on the support top. The joints should be circumferentially welded, and stiffening plates of 45*45*1cm are welded on both sides. The stiffening plates are fully circumferentially welded around the perimeter, with a weld leg height of not less than 8mm and a weld grade of Class III. The main load-bearing beam on the side of the support point should be tightly sealed with the distribution beam at the top of the support point using pads.

[0106] 5) Laying of the bottom formwork system The formwork system for pier #268 consists of a longitudinal distribution beam and a steel bottom formwork. The distribution beam is made of I-beams (16mm diameter), 12m long, and arranged 40cm apart center-to-center. It was hoisted in batches by a crawler crane and then laid and adjusted manually. Passageways and railings are provided on both sides of the distribution beam.

[0107] 5.4.2 Support preloading 1. Purpose of preloading the support By applying preload to the crossbeam support, the load-bearing capacity and stability of the support are checked. This eliminates the inelastic deformation of the support and yields elastic deformation, providing a basis for setting the pre-camber of the crossbeam bottom formwork later, ensuring that the structural alignment meets the requirements of the construction drawings and that the support is used safely.

[0108] 2. Support preloading scheme Preloading is performed using 1×1×0.9m precast concrete blocks in conjunction with 0.2t sandbags each. According to design requirements, the preloading load is 1.2 times the self-weight of the crossbeam. Preloading can only proceed after the support structure has passed inspection.

[0109] 1) Load Calculation The crossbeam construction support was preloaded as required, and the preload weight was calculated as follows: According to the analysis, the support pre-pressing needs to calculate the concrete weight of the beam. Through CAD drawing, the overall concrete volume of the 268# pier beam is 552.5m³, and the overall concrete volume of the 269# pier beam is 508.5m³. The unit weight of concrete is 2.6t / m³. Therefore, the weight of the 268# pier beam is 552.5*2.6=1436.5t, and the weight of the 269# pier beam is 508.5*2.6=1322.1t.

[0110] When the support pre-pressing is carried out, according to the design requirements, the weight of the pre-pressing is not less than 1.2 times the weight of the beam. Therefore, the weight of the 268# pier is 1.2*1436.5=1723.8t, and the weight of the 269# pier is 1.2*1322.1=1586.5t.

[0111] 2) Pre-pressing method The pre-pressing material is 1*1*0.9m concrete precast block, the weight of a single precast block is 2.2t, and the number of sand bags is supplemented. The pre-pressing is divided into 60%, 100%, and 120% three levels for pre-pressing observation.

[0112] (1) First stage loading 60% pre-pressing block distribution The pre-pressing block is 1*1*0.9m with a unit weight of 2.2t. The 268# pier is arranged with 390 blocks in 3 layers, 160 blocks in the first layer, 160 blocks in the second layer, and 70 blocks in the third layer. The remaining 3.90t is supplemented by 20 sand bags with a unit weight of 0.2t. The 269# pier is arranged with 358 blocks in 3 layers, 160 blocks in the first layer, 160 blocks in the second layer, and 38 blocks in the third layer. The remaining 5.66t is supplemented by 28 sand bags with a unit weight of 0.2t. The detailed pre-pressing block distribution diagram is as follows Figures 28-31 .

[0113] (2) Second stage loading 100% pre-pressing block distribution The pre-pressing block is 1*1*0.9m with a unit weight of 2.2t. The 268# pier is arranged with 650 blocks in 5 layers, 160 blocks in the first layer, 160 blocks in the second layer, 160 blocks in the third layer, 160 blocks in the fourth layer, and 10 blocks in the fifth layer. The remaining 6.50t is supplemented by 33 sand bags with a unit weight of 0.2t. The 269# pier is arranged with 598 blocks in 4 layers, 160 blocks in the first layer, 160 blocks in the second layer, 160 blocks in the third layer, and 118 blocks in the fourth layer. The remaining 6.50t is supplemented by 33 sand bags with a unit weight of 0.2t. The detailed pre-pressing block distribution diagram is as follows Figures 32-35 .

[0114] (3) Third stage loading 120% pre-pressing block distribution The preloading blocks are 1×1×0.9m in size, with a unit weight of 2.2t. For pier #268, a total of 780 preloading blocks are arranged in 5 layers: 160 blocks in each layer, and 140 blocks in the fifth layer. The remaining 7.80t is replenished using 39 sandbags with a unit weight of 0.2t. For pier #269, a total of 718 preloading blocks are arranged in 5 layers: 160 blocks in each layer, and 78 blocks in the fifth layer. The remaining 6.92t is replenished using 35 sandbags with a unit weight of 0.2t. See the detailed preloading block arrangement for details. Figures 36-39 .

[0115] (4) Unloading of the pre-compression block in the fourth stage After preloading to 120%, observations are taken every 6 hours. The preloading unloading time is based on the principle of stable deformation of the crossbeam support. Preloading is terminated and unloading is carried out when the difference between the average values ​​of the last two settlement observations is no greater than 2 mm. The unloading sequence is the reverse of the weight sequence, and observation records are kept. After all the weights are unloaded, the measurement data of the bracket are statistically analyzed.

[0116] Unloading should be carried out according to the principles of symmetry, layering, and grading. The first stage unloads to 100% of the design value; the second stage unloads to 60% of the design value; and the final stage unloads completely. After each stage of unloading, the system should be allowed to stand still for 1 hour and then observed before continuing unloading. Based on the measured linear and inelastic deformation, the elevation of the vertical formwork is determined, and then the elevation of the bottom formwork can be adjusted.

[0117] 3. Settlement monitoring Arrangement of settlement observation points After examining the actual site conditions and taking all factors into consideration, an observation platform was installed on top of each pillar to ensure that all observation points had a line of sight. The layout of the measurement points is shown below. Figures 40-43 .

[0118] One settlement observation point was set up on each steel pipe column to monitor the foundation settlement.

[0119] Observation requirements Before loading, the data of the bottom formwork observation points should be measured and recorded as the initial data values ​​for preloading settlement observation.

[0120] Loading process: the pre-pressing load can be loaded in three stages of 60%, 100%, 120% of the pre-pressing load, and after each loading, the vertical and lateral deformation values are measured after 1h static stop, and then the displacement of each observation point is monitored and recorded every 6 hours, when the average displacement difference of adjacent two times is not more than 2mm, the subsequent loading can be carried out, and the loading is carried out to 120%, then the displacement of each observation point is monitored and recorded every 6 hours, when the average displacement difference of continuous 12h monitoring is not more than 2mm, the settlement tends to be stable, and the unloading can be started, and the displacement of each monitoring point should be detected and recorded 6h after the support unloading. During the loading process, the measurement group personnel should use the instrument to observe the deformation and subsidence of the support, and the actual observation is the basis, when the deformation and subsidence speed is obviously accelerated, the pre-pressing should be stopped immediately, the operation personnel should be withdrawn, and the scheme should be modified and the support should be reinforced.

[0121] The above is a further detailed description of the present application in combination with the specific preferred embodiments, and the specific implementation of the present application cannot be limited to these descriptions. For those skilled in the art to which the present application belongs, without departing from the concept of the present application, a number of equivalent substitutions or obvious modifications can be made, and the performance or use is the same, which should be regarded as belonging to the protection scope of the present application.

Claims

1. A two-stage construction method for the crossbeam under the pylon of a cable-stayed bridge, characterized in that... Includes the following steps: S1: Construction tower base (1) and the base (201) of the tower body of the tower column (2) located on the tower base (1). S2: Cast the tower column (2) along the base (201) of the tower body, without first casting the support segment (202) spliced ​​with the lower crossbeam (3). The casting of the support segment (202) is postponed until after the construction of the lower crossbeam (3) is completed. S3: Install the lower crossbeam support (4) between the two tower columns (2), install the lower crossbeam formwork system (5) on the lower crossbeam support (4), and tie the steel reinforcement skeleton of the intersection area of ​​the lower crossbeam (3) and the support segment (202); S4: Set up a fixed steel mold in the area where the support segment (202) is located. The top surface of the fixed steel mold is spliced ​​with the bottom mold of the template system (5). The backfill sand mold (7) in the area enclosed by the fixed steel mold is placed on the bottom surface of the cantilever end of the lower beam (3) after pouring, as well as the bottom surface of the end mold and side mold of the lower beam template system (5). S5: The lower crossbeam (3) adopts the post-tensioned prestressed concrete construction process. The lower crossbeam (3) is reserved with the first stage steel strand tensioning duct (301) and the second stage steel strand tensioning duct (302). The steel strands passing through the first stage steel strand tensioning duct (301) are tensioned after the concrete of the lower crossbeam (3) is poured and the actual strength of the concrete increases to the percentage preset value of the design value. Before tensioning, the lower crossbeam formwork system (5) is removed, and only the bottom formwork is retained. After tensioning is completed, the duct is grouted. S6: Remove the sand mold (7) and dismantle the fixed steel mold in the area where the support segment (202) is located, and completely transfer the concrete load of the lower beam to the support of the lower beam bracket (4); S7: Tie the remaining steel reinforcement skeleton of the support segment (202), then erect the formwork and pour the support segment (202). The support segment (202) and the lower crossbeam (3) are poured as a whole. The steel strand tensioning duct reserved on the support segment (202) is connected to the second stage steel strand tensioning duct (302) of the lower crossbeam (3). When the actual strength of the concrete increases to the percentage preset value of the design value, tensioning is carried out. Before tensioning, the formwork is removed. After tensioning is completed, the duct is grouted. S8: Remove the lower crossbeam support (4).

2. The two-stage construction method for the lower crossbeam of the cable-stayed bridge tower according to claim 1, characterized in that... The tower column (2) is a zigzag inclined type, which is constructed by segmented casting. The upper segment is supported by the lower segment. The support segment (202) expands outward below and shrinks inward above. There are two segments between the support segment (202) and the root of the tower body (201).

3. The two-stage construction method for the lower crossbeam of the cable-stayed bridge tower according to claim 1, characterized in that... The steel reinforcement cage of the lower beam (3) has pre-reserved anchoring steel bars at both ends extending into the area where the support segment (202) to be poured is located.

4. The two-stage construction method for the lower crossbeam of the cable-stayed bridge tower according to claim 1, characterized in that... The first stage of prestressing tensioning uses ordinary anchorages; the second stage of prestressing tensioning uses deep-buried anchorages. The outer side of the support segment (202) is reserved with a sealing groove for pouring a sealing concrete slab (6) to connect the deep-buried anchorages.

5. The two-stage construction method for the lower crossbeam of the cable-stayed bridge tower according to claim 1, characterized in that... The sand mold (7) is filled with sand and compacted, and the top surface of the sand layer is leveled with cement mortar.

6. The two-stage construction method for the lower crossbeam of the cable-stayed bridge tower according to claim 1, characterized in that... The first stage steel strand tensioning duct (301) is arranged in the core area at the bottom of the lower crossbeam to tension the arch; the second stage steel strand tensioning duct (302) is arranged in the edge area at the bottom of the lower crossbeam and the upper area of ​​the lower crossbeam.

7. The two-stage construction method for the lower crossbeam of the cable-stayed bridge tower according to claim 4, characterized in that... In the first and second stages of prestressing tensioning, tension control adopts dual control of tension force and elongation value, with stress control as the main method and elongation value as the verification method. In the first stage, after the concrete reaches 95% of its design strength, a total of 16 prestressed steel strands are tensioned and anchored at the end of the lower crossbeam interface. In the second stage, a total of 72 prestressed steel strands are tensioned and anchored on the outer wall of the tower column. All prestressed steel strands are formed using circular corrugated metal pipes.

8. The two-stage construction method for the lower crossbeam of the cable-stayed bridge tower according to claim 5, characterized in that... The backfilling sand is medium sand with a particle size of 0.075 to 4.75 mm. The sand moisture content should not exceed 5% and the mud content should not exceed 2%. The backfilling should be compacted in layers. The thickness of a single backfill should not exceed 30 cm. During the compaction process, water should be sprinkled to compact it. After backfilling to 20 cm from the bottom chamfer of the lower beam, the bearing capacity test should be carried out. The bearing capacity should not be less than 180 kPa. Finally, a 20 cm thick cement mortar should be applied to level it and placed on the part of the bottom formwork that is cantilevered from the lower beam (3).

9. The two-stage construction method for the lower crossbeam of the cable-stayed bridge tower according to claim 1, characterized in that... After the lower crossbeam support (4) is installed, it is preloaded. The surcharge material is preloaded using 1×1×0.9m precast concrete blocks. The weight of a single precast block is 2.2t. Sandbags are used to supplement the remaining blocks. The preloading is carried out in three levels: 60%, 100%, and 120%. Deformation observation and statistical analysis are carried out during the preloading process. After preloading is completed, unloading should be carried out according to the principles of symmetry, layering, and grading. The first stage unloads to 100% of the design value; the second stage unloads to 60% of the design value; and the last stage unloads completely. After unloading to the next stage, the system should be stopped for 1 hour and observed once. Then unloading can continue. Based on the measured linear and inelastic deformation, the elevation of the vertical formwork can be determined, and the elevation of the bottom formwork can be adjusted.

10. The two-stage construction method for the lower crossbeam of the cable-stayed bridge tower according to claim 9, characterized in that... Before loading, the data of the bottom formwork observation points should be measured and recorded as the initial data values ​​for preloading settlement observation; After each loading, stop for 1 hour to measure the vertical and lateral deformation values. Then, monitor and record the displacement of each observation point at 6-hour intervals. Loading can only proceed if the difference between the average displacement of two consecutive monitoring measurements is no greater than 2mm. After loading to 120%, monitor and record the displacement of each observation point at 6-hour intervals. Settlement can be considered to be stable and unloading can begin when the difference between the average displacement of 12 consecutive hours is no greater than 2mm. The displacement of each monitoring point should be measured and recorded 6 hours after the support is unloaded. During the loading process, the measurement team should use instruments to observe the deformation and sinking of the support. The specific observations should be based on actual observations. If the deformation and sinking rate is found to be significantly accelerated, the preloading should be stopped immediately, the workers should be evacuated, and the plan should be modified and the support reinforced.

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