Top falling beam portal structure and cast-in-place beam top beam transformation method

Abstract

The invention discloses a top falling beam portal structure and a cast-in-place beam top beam transformation method.The top falling beam portal structure comprises a first top falling beam portal and a second top falling beam portal, and the first top falling beam portal comprises a bottom frame and a supporting structure located on the bottom frame; the bottom frame surrounds a bridge body of the first pier, the supporting structure is located on the side close to a cast-in-place beam and fixed to the bottom frame, and the supporting structure comprises a first main beam, a first telescopic sleeve assembly and a first hydraulic cylinder assembly; the second top falling beam portal is of an n-shaped structure and comprises a second main beam, a second telescopic sleeve assembly, a second lower bearing beam and a second hydraulic cylinder assembly. Through cooperation of the first jacking and falling beam portal and the second jacking and falling beam portal, two sets of cast-in-place beams with different pier heights can be jacked in a limited mode, and meanwhile adjustment after jacking can be facilitated through the first telescopic sleeve assembly and the second telescopic sleeve assembly.

Description

Technical Field

[0001] The invention belongs to the technical field of bridge construction, and in particular relates to a top-drop beam portal structure and a cast-in-place beam top beam reconstruction method. Background Art

[0002] Jianqu Tashiwu Middle Bridge is located in Jiande City, Zhejiang Province. The bridge is 62.515m long, with a span of 2-24m single-track simply supported box girder. The starting and ending mileages are JQDK2+793.76~+856.275. Its position is under the Hangzhou-Huangshan Railway, with an angle of 39 degrees. The bottom elevation of the Hangzhou-Huangshan beam is 84.216m, and the track elevation of Jianqu under the Hangzhou-Huangshan connecting line is 76.599m, with a height difference of 7.617m.

[0003] The cast-in-place beam that has been cast is a 24m single-line simply supported box beam, with a beam length of 24.6m, a top width of 7.6m, a bottom width of 3.0m, a support centerline distance of 0.75m from the beam end, and a support transverse width of 2.3m. Figure 1 As shown, the cast-in-place beams, the first pier and the second pier of the Tashiwu Middle Bridge are displayed. The first pier is a single-column pier, and the second pier is a stepped base adjacent to the road surface.

[0004] Now it is necessary to carry out jacking and reconstruction operations on the cast-in-place beams that have been cast, involving jacking of cast-in-place beams, pier reconstruction and beam dropping, etc. The bridge jacking generally adopts an overall hydraulic synchronous lifting scheme, that is, the original bridge piers are used to bear the load without damaging the original bridge deck pavement. First, the hydraulic jacking device is used to support the bridge superstructure as a whole, and then the columns under the piers and cap beams are cut off, and then the hydraulic jacking device is used to raise it to the designed height, and finally the column steel bars are connected to set up the formwork to pour the second phase of concrete.

[0005] However, this method is Figure 1 For the Tashiwu Middle Bridge on display, it is difficult to bear the load through the piers themselves; at the same time, it is difficult to adapt to the situation where the piers at both ends have inconsistent heights. When the pier at one end is higher, it is difficult to arrange the hydraulic jacking device; at the same time, the installation of the hydraulic jacking device can easily affect the installation and removal of the pier body formwork. Summary of the invention

[0006] The object of the present invention is to provide a top-drop beam gantry structure and a cast-in-place beam top beam reconstruction method to solve the problems existing in the background technology.

[0007] The objective of the present invention is achieved through the following technical solutions: A top-drop beam gantry structure is used for lifting a cast-in-place beam. A first pier and a second pier are provided at the bottom of the cast-in-place beam. The length of the first pier is greater than that of the second pier. The structure comprises a first top-drop beam gantry and a second top-drop beam gantry. The first top-drop beam gantry comprises a bottom frame and a supporting structure located on the bottom frame. The bottom frame surrounds the bridge body of the first pier. The supporting structure is located on a side close to the cast-in-place beam and is fixed to the bottom frame. The supporting structure comprises a first main beam, a first telescopic sleeve assembly and a first hydraulic cylinder assembly. The second top-drop beam gantry is a Π-shaped structure, and the second top-drop beam gantry is located on both sides of the abutment of the second pier. The second top-drop beam gantry includes a second main beam, a second telescopic sleeve assembly, a second lower beam and a second hydraulic cylinder assembly.

[0008] Furthermore, the bottom frame is located on the pedestal of the first pier, and the bottom frame includes a first lower pad beam, an anchor beam, a column and an extension beam. A first diagonal brace is provided between the anchor beam and the first lower pad beam, a second diagonal brace is provided between the extension beam and the first lower pad beam, and a third diagonal brace is provided between the first main beam and the extension beam.

[0009] Furthermore, the axis of the first main beam is perpendicular to the axis of the cast-in-place beam, two first telescopic sleeve assemblies are respectively located on both sides of the first main beam, and one side of each first telescopic sleeve assembly corresponds to a first hydraulic cylinder assembly.

[0010] Furthermore, the second telescopic sleeve assembly includes a second telescopic inner sleeve and a second telescopic outer sleeve, the second telescopic inner sleeve is fixed to the lower end of the second main beam, the second telescopic outer sleeve is fixed to the second lower beam, and the second telescopic outer sleeve is also provided with a second outer sleeve extension section, the second outer sleeve extension section is a split structure, the split of the second outer sleeve extension section is connected by bolts and is sleeved outside the second telescopic inner sleeve, and the second outer sleeve extension section is connected to the second telescopic outer sleeve by bolts.

[0011] Furthermore, the first telescopic sleeve assembly has the same structure as the second telescopic sleeve assembly, and the first telescopic sleeve assembly includes a first telescopic inner sleeve, a first telescopic outer sleeve and a first outer sleeve extension section.

[0012] Furthermore, two groups of the second lower pad beams are respectively located on both sides of the second pier, the axial direction of the second lower pad beams is the same as the axial direction of the cast-in-place beams, and a high-position diagonal brace is provided between the second main beam and the second lower pad beams.

[0013] Furthermore, the axis of the second main beam is perpendicular to the axis of the cast-in-place beam, two second telescopic sleeve assemblies are respectively located on both sides of the second main beam, both ends of the second telescopic sleeve assembly are respectively connected to the second main beam and the second lower beam, and one side of each second telescopic sleeve assembly corresponds to a second hydraulic cylinder assembly.

[0014] A method for transforming a top beam of a cast-in-place beam comprises the following steps: S1: Use the slope excavation method to dig out the backfill soil above the top of the first and second pier caps; S2: Install the first top beam drop portal frame and the second top beam drop portal frame at the same time; S3: Test lifting, remove all the bolts between all the supports of the cast-in-place beam and the embedded plates of the supports, control the first hydraulic cylinder assembly and the second hydraulic cylinder assembly to test lift, and the two gantries first test lift 10mm and then stop for 5 minutes for observation; S4: Formal lifting, control the first hydraulic cylinder assembly and the second hydraulic cylinder assembly to lift synchronously, lift synchronously to 200mm, lift speed is 0.2m / min, and add a set of outer sleeve extension sections to the exposed telescopic inner sleeve; S5: Repeat step S4, lift the main beam of the portal frame by 600 mm, retract the hydraulic cylinder, support the cast-in-place beam through the jacket extension section and the telescopic jacket, and add a pier at the bottom of the hydraulic cylinder; S6: Repeat steps S4 and S5 to complete the lifting to the designed height; S7: Pier body reconstruction, platform top and platform cap reconstruction; S8: beam dropping operation; S9: Use soil to backfill and compact the base area of ​​the first pier and the second pier.

[0015] Furthermore, step S7 of pier body transformation includes sub-steps S71-S74: S71: Remove the concrete within 3.3m below the existing pier cap and chisel away the concrete within 70cm below; S72: Clean and rinse the steel bars, weld and connect the main bars and tie the stirrups; S73: Install the pier cap formwork, tie the pier cap reinforcement and pre-buried pad stone reinforcement, and pour the pier cap concrete; S74: Pier cap maintenance, formwork erection and pouring of pad stone concrete.

[0016] Furthermore, the modification of the top and cap of the platform in step S7 includes sub-steps S75-S77: S75: Chisel away the existing platform top and platform cap concrete; S76: Clean and rinse the main reinforcement, install the platform top and platform cap template, weld and connect the main reinforcement, tie the steel bars, and embed the pad stone steel bars; S77: Casting of platform cap and platform top concrete, maintenance, formwork erection and casting of pad stone concrete.

[0017] The beneficial effects of the present invention are: 1) Through the cooperation of the first top-drop beam gantry and the second top-drop beam gantry structure, the cast-in-place beams of two groups of piers with different heights can be lifted to a limited extent. At the same time, the first telescopic sleeve assembly and the second telescopic sleeve assembly can facilitate adjustment after lifting.

[0018] 2) The first beam-dropping gantry is raised and supported by the bottom frame, which facilitates the first main beam, the first telescopic sleeve assembly and the first hydraulic cylinder assembly in the supporting structure to lift the cast-in-place beam attached to the first pier. At the same time, the supporting structure is only located on one side of the bottom frame close to the cast-in-place beam, which does not affect the installation and removal of the formwork.

[0019] 3) The extended beam is connected to the first lower pad beam and the first main beam through the second diagonal brace and the third diagonal brace respectively, so as to strengthen the ability of the first top beam gantry to resist the horizontal load in the longitudinal direction of the bridge when supporting the cast-in-place beam. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of a cast-in-place beam in the background technology of the present invention; Figure 2 It is a working schematic diagram of the present invention when jacking is performed through the jacking beam gantry structure; Figure 3 It is a front view of the first top beam door frame of the present invention; Figure 4 It is a side view of the first top beam door frame of the present invention; Figure 5 It is a middle plane view of the first top beam door frame of the present invention; Figure 6 It is a front view of the second top beam door frame of the present invention; Figure 7 It is a side view of the second top beam door frame of the present invention; Figure 8 A top view of the second telescopic inner sleeve and the second outer sleeve extension section of the present invention; In the figure, 1-cast-in-place beam, 2-first pier, 3-second pier, 4-first top-drop beam gantry, 41-first lower pad beam, 42-column, 43-anchor beam, 44-extending beam, 45-first main beam, 46-first diagonal brace, 47-second diagonal brace, 48-third diagonal brace, 49-first hydraulic cylinder assembly, 5-second top-drop beam gantry, 51-second lower pad beam, 52-second main beam, 53-high-position diagonal brace, 54-second hydraulic cylinder assembly, 6-second telescopic sleeve assembly, 61-second telescopic inner sleeve, 62-second outer sleeve extension section, 63-second telescopic outer sleeve, 7-first telescopic sleeve assembly. DETAILED DESCRIPTION

[0021] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0022] like Figure 1 As shown, the bottom of the cast-in-place beam 1 is supported by the first pier 2 and the second pier 3, wherein the first pier 2 is a single-column pier, and the second pier 3 is a stepped base adjacent to the road surface. The overall height of the second pier 3 is much lower than the overall height of the first pier 2, and the traditional jacking method cannot be used for jacking at this time.

[0023] Example 1 See also Figure 2-Figure 8 The present invention provides a technical solution: a top-drop beam gantry structure for Figure 1 The lifting of the middle cast-in-place beam 1 includes a first lifting beam gantry 4 and a second lifting beam gantry 5. The first lifting beam gantry 4 includes a bottom frame and a supporting structure located on the bottom frame. The bottom frame surrounds the bridge body of the first pier 2. The supporting structure is located on a side close to the cast-in-place beam 1 and is fixed to the bottom frame. The supporting structure includes a first main beam 45, a first telescopic sleeve assembly 7 and a first hydraulic cylinder assembly 49. The second top-drop beam gantry 5 is a Π-shaped structure. The second top-drop beam gantry 5 is located on both sides of the abutment of the second pier 3. The second top-drop beam gantry 5 includes a second main beam 52, a second telescopic sleeve assembly 6, a second lower pad beam 51 and a second hydraulic cylinder assembly 54.

[0024] Through the above technical solution, the first beam-dropping gantry 4 is raised and supported by the bottom frame, which facilitates the first main beam 45, the first telescopic sleeve assembly 7 and the first hydraulic cylinder assembly 49 in the supporting structure to lift the cast-in-place beam 1 attached to the first pier 2. At the same time, the supporting structure is only located on one side of the bottom frame close to the cast-in-place beam 1, which does not affect the template installation and removal construction. The structure of the second pier 3 is a stepped type. In order to facilitate the lifting of the cast-in-place beam 1 attached to the second pier 3, the second beam-dropping gantry 5 adopts a Π-shaped structure and is arranged on both sides of the bridge body.

[0025] The first main beam 45 and the second main beam 52 are respectively located below the cast-in-place beam 1 to support the cast-in-place beam 1. The first main beam 45 and the second main beam 52 are respectively lifted by the first telescopic set assembly 7 and the second telescopic set assembly 6 below, thereby lifting the cast-in-place beam 1. The first lifting beam gantry 4 and the second lifting beam gantry 5 can lift the cast-in-place beams 1 of two groups of piers with different heights to a limited extent, and the first telescopic set assembly 7 and the second telescopic set assembly 6 can facilitate adjustment after lifting.

[0026] Furthermore, the bottom frame is located on the pedestal of the first pier 2, and the bottom frame includes a first lower pad beam 41, an anchor beam 43, a column 42 and an extension beam 44. The frame structure is formed by the first lower pad beam 41, the anchor beam 43 and the column 42, and is supported and fixed by a first diagonal brace 46. The extension beam 44 is respectively connected to the first lower pad beam 41 and the first main beam 45 by a second diagonal brace 47 and a third diagonal brace 48, thereby strengthening the ability of the first top-drop beam gantry 4 to resist the longitudinal horizontal load of the bridge during the period of supporting the cast-in-place beam 1.

[0027] Furthermore, the axis of the first main beam 45 is perpendicular to the axis of the cast-in-place beam 1 , and the two first telescopic sleeve assemblies 7 are respectively located on both sides of the first main beam 45 , and one side of each first telescopic sleeve assembly 7 corresponds to a first hydraulic cylinder assembly 49 .

[0028] The second telescopic sleeve assembly 6 includes a second telescopic inner sleeve 61 and a second telescopic outer sleeve 63. The second telescopic inner sleeve 61 is fixed to the lower end of the second main beam 52. The second telescopic outer sleeve 63 is fixed to the second lower beam 51. The second telescopic outer sleeve 63 is also provided with a second outer sleeve extension section 62. The second outer sleeve extension section 62 is a split structure. The split of the second outer sleeve extension section 62 is connected by bolts and is sleeved outside the second telescopic inner sleeve 61. The second outer sleeve extension section 62 is connected to the second telescopic outer sleeve 63 by bolts.

[0029] Through the above technical solution, see Figure 6-Figure 8 The second telescopic inner sleeve 61 is fixed to the bottom of the second main beam 52, and the second telescopic outer sleeve 63 is fixed on the second lower pad beam 51 and sleeved outside the second telescopic inner sleeve 61. When the second main beam 52 is lifted a certain distance by the second hydraulic cylinder assembly 54, the second telescopic inner sleeve 61 extends out of the second telescopic outer sleeve 63 for a certain distance, and is sleeved on the second telescopic inner sleeve 61 after being connected by bolts through the split second outer sleeve extension section 62. Then, the added second outer sleeve extension section 62 is fixed to the second telescopic outer sleeve 63 below, until it is lifted to a suitable position, and then the uppermost second outer sleeve extension section 62 is fixed to the second main beam 52. At this time, the second main beam 52, the second outer sleeve extension section 62 and the second lower pad beam 51 are fixed as a whole.

[0030] The first telescopic sleeve assembly 7 has the same structure as the second telescopic sleeve assembly 6. The first telescopic sleeve assembly 7 includes a first telescopic inner sleeve, a first telescopic outer sleeve and a first outer sleeve extension section. The working principle of the first telescopic sleeve assembly 7 is the same as above.

[0031] Furthermore, two groups of the second lower pad beams 51 are respectively located on both sides of the second pier 3 , the axial direction of the second lower pad beams 51 is the same as the axial direction of the cast-in-place beam 1 , and a high-position diagonal brace 53 is provided between the second main beam 52 and the second lower pad beam 51 .

[0032] Furthermore, the axis of the second main beam 52 is perpendicular to the axis of the cast-in-place beam 1, and the two second telescopic set assemblies 6 are respectively located on both sides of the second main beam 52, and the two ends of the second telescopic set assembly 6 are respectively connected to the second main beam 52 and the second lower beam 51, and one side of each second telescopic set assembly 6 corresponds to a second hydraulic cylinder assembly 54.

[0033] Through the above technical solution, the second lower pad beam 51 is located on the pedestal of the second pier 3, and a supporting structure is formed by the second lower pad beam 51, the second telescopic sleeve assembly 6 and the second main beam 52. At the same time, the second main beam 52 and the second lower pad beam 51 are connected and supported by the high-position diagonal brace 53.

[0034] Example 2 A method for transforming a top beam of a cast-in-place beam comprises the following steps: S1: Use the slope excavation method to dig out the backfill soil above the top of the first pier 2 and the second pier 3. At the same time, the existing concrete railings can be removed using the skylight points to facilitate subsequent construction.

[0035] S2: The installation of the first top beam door frame 4 and the second top beam door frame 5 can be performed with reference to the structure of Example 1; The first top beam-dropping gantry 4 adopts a supporting structure of bottom frame + upper single beam and double upright legs. The top surface of the bottom frame is 20cm away from the pier chiseling line, and the bottom is located on the pedestal. The longitudinal bridge direction is wedged and anchored with the pier body through the frame longitudinal beam and fine-rolled threaded steel. In the space above the pier chiseling line and below the elevated pier cap, the supporting structure is located on the side with the beam, and no gantry components are arranged on the other three sides, which is convenient for the pier cutting / chiseling construction. Within this range, there are only two leg columns 42 and their outer diagonal braces on the side of the pier with the beam. The leg columns 42 are 1m away from the pier cap, which can meet the requirements of template installation and removal construction. The first hydraulic cylinder assembly 49 includes a total of 4 100t hydraulic cylinders.

[0036] The second top drop beam gantry 5 is a Π-shaped structure, the second lower pad beam 51 is anchored on the pedestal, the second hydraulic cylinder assembly 54 includes a total of 4 63t hydraulic cylinders, the upper ends of the hydraulic cylinders are connected to the ear plates on both sides of the beam ends of the second main beam 52, and the lower ends are supported on the second lower pad beam 51 / pad pier.

[0037] S3: Trial lifting, remove all the bolts between all the supports of the cast-in-place beam 1 and the embedded plates of the supports, control the first hydraulic cylinder assembly 49 and the second hydraulic cylinder assembly 54 to perform trial lifting, and the two gantries first perform a trial lifting of 10 mm and then stop for 5 minutes for observation; S4: Formal lifting, control the first hydraulic cylinder assembly 49 and the second hydraulic cylinder assembly 54 to lift synchronously, lift synchronously to 200 mm, lift speed is 0.2 m / min, and a set of outer sleeve extension sections are added to the exposed telescopic inner sleeve; S5: Repeat step S4, lift the main beam of the portal frame by 600 mm, retract the hydraulic cylinder, support the cast-in-place beam 1 through the jacket extension section and the telescopic jacket, and add a pier at the bottom of the hydraulic cylinder; S6: Repeat steps S4 and S5 to complete the lifting to the designed height; S7: Pier body reconstruction, platform top and platform cap reconstruction; The pier body reconstruction includes sub-steps S71-S74: S71: Cut off the concrete within 3.3m below the top of the existing pier cap, and chisel off the concrete within 70cm below. When chiseling, first use a chalk line to mark the lowest elevation line to be chiseled on the surface of the pier body, and then use a cutting machine to cut 3 to 5mm deep around to reduce damage to the concrete on the joint surface during chiseling.

[0038] S72: Clean and rinse the steel bars, weld and connect the main bars and tie the stirrups; S73: Install the pier cap formwork, tie the pier cap reinforcement and the pre-buried pad stone reinforcement, pour the pier cap concrete, use the standard steel formwork for the pier body, evenly paint the inner surface of the formwork, install it in blocks, fix it up and down and left and right with bolts, pull it longitudinally and around with precision-rolled threaded steel, and paste double-sided tape on the inner surface of the steel formwork at the joint to ensure that the steel formwork joint is tightly attached and does not leak; S74: Pier cap maintenance, formwork erection and pouring of pad stone concrete.

[0039] The table top and table cap modification includes sub-steps S75-S77: S75: Chisel away the existing platform top and platform cap concrete; S76: Clean and rinse the main reinforcement, install the platform top and platform cap template, weld and connect the main reinforcement, tie the steel bars, and embed the pad stone steel bars; S77: Casting of platform cap and platform top concrete, maintenance, formwork erection and casting of pad stone concrete.

[0040] S8: Beam dropping operation; drop the cast-in-place beam 1 onto the three-dimensional beam dropping device. The steps of the beam dropping operation are opposite to those of the beam lifting operation. The three-dimensional beam dropping device is installed on the inner side of the pier and the platform pad stone. A 200t lifting jack is installed in each set of three-dimensional beam dropping device as a vertical supporting structure. The two sets of supporting structures on the top of one pier are set as two independent fulcrums, and the two sets of supporting structures on the top of the other pier are a balanced fulcrum. The four fulcrums are a four-point support and three-point balanced support method.

[0041] The two independent fulcrums of the three-dimensional beam-dropping device are to connect the oil inlet and outlet ports of the two vertical jacks on a bridge pier with a high-pressure oil pump to supply oil respectively. According to the design elevation, the top height of the piston is determined. A hydraulically controlled one-way valve is set on the oil inlet line of the jack to maintain the position of the jack rod, thereby maintaining the lifting pressure. A balanced fulcrum of the three-dimensional beam-dropping device is to connect the oil inlet and outlet ports of the two jacks on the left and right sides of the other pier top with a tee, and use a high-pressure oil pump to supply oil together, so that the two jacks move in a balanced manner, and the top height of the piston is determined by the external load, so as to maintain the balanced support of the load of the two jacks. The connecting pipelines between the two jacks on both sides of the pier top are connected with steel pipes, and a hydraulically controlled one-way valve is set on the main tee line to maintain the position of the jack rod, thereby maintaining the lifting pressure. The independent fulcrum and the balanced fulcrum high-pressure oil pump are placed on the two piers of the hole to be erected.

[0042] The transverse movement system of the three-dimensional beam-dropping device is equipped with 50t jacks along the longitudinal and transverse directions of the bridge as longitudinal and transverse translation driving devices. The longitudinal and transverse movement strokes of the transverse movement system are, and the front, back, left and right frames are set to limit the movement range of the slide plate, so there is no need to set other limit devices. The horizontal reaction force of the jack acts on the outer wall of the device, which is the internal force of the device. No additional embedded parts are required between the three-dimensional beam-dropping device and the bridge pier. When moving the beam forward along the bridge direction, the longitudinal jacking jacks in the first two three-dimensional beam-dropping devices are used to push the concrete box beam forward. When moving the beam to the left or right in the transverse direction of the bridge, the transverse jacking jacks in the two three-dimensional beam-dropping devices on the left or right are used to push the concrete box beam to the left or right respectively.

[0043] After the box girder is dropped to the three-dimensional beam-dropping device through the top beam-dropping portal, the vertical, longitudinal and transverse jacks of the three-dimensional beam-dropping device are used to adjust the vertical, longitudinal and transverse positions of the box girder to put the box girder in place. Then, the support grouting operation is carried out according to the conventional beam erection operation process. After the grout is filled and reaches the designed allowable strength, the three-dimensional beam-dropping device is removed.

[0044] S9: Backfill and compact the base areas of the first pier 2 and the second pier 3 with soil.

[0045] The above is only a preferred embodiment of the present invention. It should be understood that the present invention is not limited to the form disclosed herein, and should not be regarded as excluding other embodiments, but can be used in various other combinations, modifications and environments, and can be modified within the scope of the concept described herein through the above teachings or the technology or knowledge of the relevant field. The changes and modifications made by those skilled in the art do not depart from the spirit and scope of the present invention, and should be within the scope of protection of the claims attached to the present invention.

Claims

1. A jacking beam gantry structure, used for jacking up a cast-in-place beam (1), wherein a first pier (2) and a second pier (3) are provided at the bottom of the cast-in-place beam, wherein the length of the first pier (2) is greater than the length of the second pier (3), and wherein: The bridge comprises a first top-drop beam gantry (4) and a second top-drop beam gantry (5), wherein the first top-drop beam gantry (4) comprises a bottom frame and a support structure located on the bottom frame, the bottom frame surrounds the outside of the bridge body of the first pier (2), the support structure is located on a side close to the cast-in-place beam and is fixed to the bottom frame, and the support structure comprises a first main beam (45), a first telescopic sleeve assembly (7) and a first hydraulic cylinder assembly (49); The second top-drop beam gantry (5) is a Π-shaped structure. The second top-drop beam gantry (5) is located on both sides of the abutment of the second pier (3). The second top-drop beam gantry (5) comprises a second main beam (52), a second telescopic sleeve assembly (6), a second lower pad beam (51) and a second hydraulic cylinder assembly (54).

2. The top-drop beam gantry structure according to claim 1 is characterized in that: The bottom frame is located on the pedestal of the first pier (2), and comprises a first lower pad beam (41), an anchor beam (43), a column (42), and an extended beam (44); a first diagonal brace (46) is provided between the anchor beam (43) and the first lower pad beam (41); a second diagonal brace (47) is provided between the extended beam (44) and the first lower pad beam (41); and a third diagonal brace (48) is provided between the first main beam (45) and the extended beam (44).

3. The top-drop beam gantry structure according to claim 1 is characterized in that: The axis of the first main beam (45) is perpendicular to the axis of the cast-in-place beam (1); two first telescopic sleeve assemblies (7) are respectively located on two sides of the first main beam (45); and one side of each first telescopic sleeve assembly (7) corresponds to a first hydraulic cylinder assembly (49).

4. The top-drop beam gantry structure according to claim 1 is characterized in that: The second telescopic sleeve assembly (6) comprises a second telescopic inner sleeve (61) and a second telescopic outer sleeve (63); the second telescopic inner sleeve (61) is fixed to the lower end of the second main beam (52); the second telescopic outer sleeve (63) is fixed to the second lower pad beam (51); a second outer sleeve extension section (62) is further provided on the second telescopic outer sleeve (63); the second outer sleeve extension section (62) is a split structure; the split parts of the second outer sleeve extension section (62) are connected by bolts and sleeved outside the second telescopic inner sleeve (61); the second outer sleeve extension section (62) is connected to the second telescopic outer sleeve (63) by bolts.

5. The top-drop beam gantry structure according to claim 4 is characterized in that: The first telescopic sleeve assembly (7) has the same structure as the second telescopic sleeve assembly (6), and the first telescopic sleeve assembly (7) comprises a first telescopic inner sleeve, a first telescopic outer sleeve and a first outer sleeve extension section.

6. The top-drop beam gantry structure according to claim 1 is characterized in that: Two groups of the second lower pad beams (51) are respectively located on both sides of the second pier (3); the axial direction of the second lower pad beams (51) is the same as the axial direction of the cast-in-place beam (1); and a high-position diagonal brace (53) is provided between the second main beam (52) and the second lower pad beam (51).

7. The top-drop beam gantry structure according to claim 1 is characterized in that: The axis of the second main beam (52) is perpendicular to the axis of the cast-in-place beam (1); two second telescopic sleeve assemblies (6) are respectively located on both sides of the second main beam (52); two ends of the second telescopic sleeve assembly (6) are respectively connected to the second main beam (52) and the second lower beam (51); and one side of each second telescopic sleeve assembly (6) corresponds to a second hydraulic cylinder assembly (54).

8. A method for reconstructing a top beam of a cast-in-place beam, comprising the top beam portal structure according to any one of claims 1 to 7, characterized in that: The following steps are involved: S1: using a slope excavation method, excavating the backfill soil within the range of the top of the first bridge pier (2) and the second bridge pier (3); S2: installing the first top beam-dropping gantry (4) and the second top beam-dropping gantry (5) at the same time; S3: Trial lifting, all bolts between all supports of the cast-in-place beam (1) and the embedded support plates are removed, and the first hydraulic cylinder assembly (49) and the second hydraulic cylinder assembly (54) are controlled to perform trial lifting, and the two portal frames are first tested to lift 10 mm and then stopped for 5 minutes for observation; S4: formal lifting, controlling the first hydraulic cylinder assembly (49) and the second hydraulic cylinder assembly (54) to lift synchronously, lifting synchronously to 200 mm, with a lifting speed of 0.2 m / min, and adding a set of outer sleeve extension sections to the exposed telescopic inner sleeve; S5: Repeat step S4, lift the main beam of the portal frame by 600 mm, retract the hydraulic cylinder, support the cast-in-place beam (1) through the jacket extension section and the telescopic jacket, and add a pier at the bottom of the hydraulic cylinder; S6: Repeat steps S4 and S5 to complete the lifting to the designed height; S7: Pier body reconstruction, platform top and platform cap reconstruction; S8: beam dropping operation; S9: backfilling and compacting the base area of ​​the first bridge pier (2) and the second bridge pier (3) with soil.

9. The cast-in-place top beam reconstruction method according to claim 8, characterized in that: Step S7: Pier body reconstruction includes sub-steps S71-S74: S71: Remove the concrete within 3.3m below the existing pier cap and chisel away the concrete within 70cm below; S72: Clean and rinse the steel bars, weld and connect the main bars and tie the stirrups; S73: Install the pier cap formwork, tie the pier cap reinforcement and pre-buried pad stone reinforcement, and pour the pier cap concrete; S74: Pier cap maintenance, formwork erection and pouring of pad stone concrete.

10. The method for reconstructing the top beam of a cast-in-place beam (1) according to claim 8, characterized in that: The modification of the top and cap of the platform in step S7 includes sub-steps S75-S77: S75: Chisel away the existing platform top and platform cap concrete; S76: Clean and rinse the main reinforcement, install the platform top and platform cap template, weld and connect the main reinforcement, tie the steel bars, and embed the pad stone steel bars; S77: Casting of platform cap and platform top concrete, maintenance, formwork erection and casting of pad stone concrete.

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