Supporting steel platform structure and construction method of large cantilever high altitude over-limit cast-in-place beam and slab

Abstract

The present invention relates to the field of building engineering technology, and discloses a supporting steel platform structure and construction method for large cantilevered high-altitude over-limit cast-in-place beams and slabs. The supporting steel platform is a space steel structure cantilever platform composed of a plurality of single-layer support frames and a plurality of double-layer support frames arranged in a row and combined. When the cantilever length of the upper cast-in-place beam and slab is greater than 4.5m or the concentrated load of the beam and slab is greater than or equal to 20kN / m, a double-layer support frame is provided, otherwise a single-layer support frame is provided; the double-layer support frame includes a main cantilever beam, a secondary cantilever beam, the first, second, third, fourth, fifth and sixth diagonal braces, and the single-layer support frame includes a main cantilever beam, the fifth and sixth diagonal braces, and is also provided with a cantilever beam connecting beam and a diagonal brace connecting beam. The present invention disperses the formwork load to the N-1st and N-2nd floor floors and the N-3rd floor side beams, and the platform has small deformation, small impact on the main structure of the building, has sufficient stability and bearing capacity, is convenient for installation and removal, has a fast construction progress, and has a low engineering cost, and effectively solves the construction problem of large cantilevered high-altitude over-limit cast-in-place beams.

Description

Technical Field

[0001] The invention relates to the technical field of building engineering, and in particular to a supporting steel platform structure of a large cantilevered high-altitude over-limit cast-in-place beam and slab and a construction method thereof. Background Art

[0002] With the diversity of architectural design, high-altitude cantilever design often appears, which cantilevers part of the roof out of the building plane. Such architectural design highlights the appearance of the building, but also brings various difficulties to the construction.

[0003] Due to the high roof beam surface of the building, if a ground-mounted steel pipe high-formwork scaffolding platform is used, the safety risks of erection and dismantling are high and the cost is high; if tie rods are installed above the steel platform, even if conditions permit, it is difficult to ensure that each tie rod can bear force at the same time, whether it is a wire rope or steel section, and the risk factor is high.

[0004] The invention patent "Construction method of high-altitude large cantilever structure" with application number 201110088550.X provides a single-layer cantilever steel triangular truss formwork platform, which adopts the method of setting a cantilever channel steel or H-shaped steel on the structural floor below the cantilever beam plate, adding a structural counter beam on the structural side and pouring concrete together with the channel steel or H-shaped steel, adding channel steel diagonal braces at the bottom and inclined channel steel in the middle to form a steel structure tripod, and then setting up secondary beam channel steel on the steel tripod, and finally setting up a common steel pipe fastener formwork frame on the secondary beam channel steel to bear all the loads of the upper cantilever beam plate. This invention solves the problem of the support system of large cantilever structures of high-altitude buildings to a certain extent, but it is only applicable to the cantilever structure construction with the cantilever beam plate of the building slightly higher than 40m above the ground and the cantilever span in the range of 2.0 to 6.0m, that is, it is only applicable to the case where the cantilever length is roughly equal to the height of the lower floor.

[0005] Especially for large cantilevered high-altitude over-limit cast-in-place beams, there are multiple difficulties in how to support them with formwork: at high altitude, the roof beam surface of the building is relatively high, and there are cases where the elevation exceeds 90m; large cantilever, the maximum cantilever length exceeds 7.5m; large load, the cross-section of the top beam exceeds a certain scale, and the concentrated line load is 20kN / m and above, which is an over-limit beam, and its concrete formwork support project belongs to the scope of the more dangerous sub-project; for the beauty of the building, the cantilevered part of the top floor is often an inclined plane, that is, the cantilever lengths of various parts are different, and the loads are also different, and it is impossible to adopt a regular steel platform structure for support.

[0006] Therefore, it is necessary to research and develop a new type of supporting steel platform structure that can meet the stability requirements of large cantilevered high-altitude over-limit cast-in-place beams. Summary of the invention

[0007] In response to the problems raised by the background technology, the present invention proposes a supporting steel platform structure and a construction method for large-cantilever high-altitude over-limit cast-in-place beams and slabs, so as to solve the problem of constructing a supporting steel platform under the conditions of high-altitude, large-cantilever, and over-limit cast-in-place beam loads to meet the requirements of stability and bearing capacity.

[0008] The supporting steel platform structure of the large cantilevered high-altitude over-limit cast-in-place beam and slab of the present invention has the following technical scheme:

[0009] The supporting steel platform is a space steel structure cantilever platform composed of a plurality of single-layer supporting frames and a plurality of double-layer supporting frames connected in a row and combined. The single-layer supporting frames and the double-layer supporting frames are used to support the cast-in-place beams and slabs of the Nth floor above. When the cantilever length of the corresponding cast-in-place beams and slabs is less than or equal to 4.5m, a single-layer supporting frame is set. When the cantilever length of the corresponding cast-in-place beams and slabs is greater than 4.5m, or when the cantilever length of the cast-in-place beams and slabs is less than or equal to 4.5m but the concentrated line load of the beams and slabs is greater than or equal to 20kN / m, a double-layer supporting frame is set.

[0010] The double-layer support frame includes a main cantilever beam installed on the N-1th layer of cast-in-place floor and cantilevered out, and a secondary cantilever beam installed on the N-2th layer of cast-in-place floor and cantilevered out, the protruding portion of the secondary cantilever beam is shorter than the protruding portion of the main cantilever beam, a first diagonal brace is fixedly installed between the end of the main cantilever beam and the end of the secondary cantilever beam, a second diagonal brace is fixedly installed between the middle of the protruding portion of the main cantilever beam and the portion of the secondary cantilever beam located at the edge of the N-2th layer of cast-in-place floor, and a middle portion of the first diagonal brace and a middle portion of the second diagonal brace are fixedly installed between the middle of the first diagonal brace and the middle of the second diagonal brace. A third diagonal brace is fixedly installed, a fourth diagonal brace is fixedly installed between the second diagonal brace and the N-1th layer cast-in-place floor edge beam, a fifth diagonal brace is fixedly installed between the end of the secondary cantilever beam and the N-3th layer cast-in-place floor edge beam, and a sixth diagonal brace is fixedly installed between the middle of the fifth diagonal brace and the N-2th layer cast-in-place floor edge beam; the main cantilever beam and its diagonal brace support the Nth layer cantilever cast-in-place floor upward, the secondary cantilever beam and its diagonal brace support the main cantilever beam and its diagonal brace upward, and the N-3th layer floor edge beam supports the secondary cantilever beam and its diagonal brace;

[0011] The single-layer support frame only includes a main cantilever beam installed on the N-1th layer of cast-in-place floor and cantilevered out, as well as a fifth diagonal brace and a sixth diagonal brace, wherein the fifth diagonal brace is fixedly installed between the end of the main cantilever beam and the N-2th layer of cast-in-place floor edge beam, and the sixth diagonal brace is fixedly installed between the middle of the fifth diagonal brace and the N-1th layer of cast-in-place floor edge beam;

[0012] A plurality of the double-layer support frames and a plurality of the single-layer support frames are connected in a row, and cantilever beam connecting beams are fixedly installed on the top of all the main cantilever beams and the top of the secondary cantilever beams, and diagonal brace connecting beams are fixedly installed in the middle of all the first diagonal braces, the middle of the second diagonal brace, and the middle of the fifth diagonal brace, respectively. The cantilever beam connecting beam and the diagonal brace connecting beam connect all the connected double-layer support frames and single-layer support frames into one.

[0013] Furthermore, the lower layer of the double-layer support frame and the single-layer support frame further include a vertical support, and the vertical support is fixedly installed between the middle of the extended part of the secondary cantilever beam of the double-layer support frame and the middle of the fifth diagonal support, or between the middle of the extended part of the main cantilever beam of the single-layer support frame and the middle of the fifth diagonal support. The vertical support is not a necessary component for the double-layer support frame and the single-layer support frame as supporting steel platform structures, but it needs to be hoisted in a semi-finished state during the installation process, so this vertical support is installed.

[0014] The following is a specific preferred method for realizing the supporting steel platform structure:

[0015] The steel materials constituting the supporting steel platform structure are all Q235B, wherein the main cantilever beam is of specification 40a, the secondary cantilever beam is of specification 32a, the diagonal braces are of specification 28a, the cantilever beam connecting beam is of specification 18, the diagonal brace connecting beam is of specification 18a# channel steel, and the vertical brace is of specification 8# channel steel.

[0016] The main cantilever beam and the secondary cantilever beam are located above the floor slab and are bolted and fixed at one end through U-bolt embedded parts in the floor slab. The main cantilever beam is welded and fixed to the I-type steel plate embedded parts at the edge of the floor slab, and the secondary cantilever beam is welded and fixed to the II-type steel plate embedded parts at the edge of the floor slab. One end of the fourth diagonal brace, the fifth diagonal brace, and the sixth diagonal brace are welded and fixed to the II-type steel plate embedded parts at the edge of the floor slab, and the connecting parts between the main cantilever beam, the secondary cantilever beam and each diagonal brace are fixed by welding.

[0017] The raw materials of the steel structure are 12m long standard steel materials to minimize on-site butt welding; when the total length of the main beam component exceeds 12m, the web is butt-welded with a 45° bevel cut, the upper and lower flanges and the web are butt-welded, and 10mm steel plates are welded and reinforced on both sides to meet the strong requirements of the raw materials; the butt node is arranged at the anchor end of the floor slab to avoid being placed at the cantilever end.

[0018] The method for constructing a supporting steel platform structure of a large cantilevered high-altitude over-limit cast-in-place beam and slab of the present invention comprises the following steps:

[0019] S1. According to the structure of the cantilevered part of the building, the supporting steel platform structure is specifically designed. According to the cantilevered length of the cast-in-place beam, a single-layer support frame or a double-layer support frame is set at the corresponding position. The material, specification, length and connection position of each steel structure are designed according to the inventive design principle;

[0020] S2, establish a finite element analysis model for the designed supporting steel platform structure, perform stability simulation calculations, appropriately adjust the material, specification, length and connection position of each steel structure according to the calculation results, and repeat the simulation calculations until all units and nodes of the supporting steel platform structure meet the stability requirements;

[0021] S3, complete the assembly of the semi-finished products of the supporting steel platform structure on the ground. The semi-finished products of the single-layer support frame include the assembled and welded main cantilever beam, the fifth diagonal brace and the vertical brace. The semi-finished products of the double-layer support frame include the upper semi-finished products and the lower semi-finished products. The upper semi-finished products include the assembled and welded main cantilever beam, the first diagonal brace, the second diagonal brace and the third diagonal brace. The lower semi-finished products include the assembled and welded secondary cantilever beam, the fifth diagonal brace and the vertical brace. Because the cantilever beams and diagonal braces of the lower semi-finished products of the double-layer support frame and the semi-finished products of the single-layer support frame are not enclosed after assembly, the cantilever beams and diagonal braces of the cantilever frame semi-finished products are easy to deform during hoisting, and 8# channel steel vertical braces are used for fixing and reinforcement;

[0022] S4, build the floor slabs of each floor, embed the I-type steel plate embedded parts, II-type steel plate embedded parts and U-type bolt embedded parts at the designed position, hoist the semi-finished product of the supporting steel platform structure, install the fourth diagonal brace and the sixth diagonal brace that have not been installed in the semi-finished product, install, complete the welding or bolting between each steel structure and between the floor slabs, install the cantilever beam connecting beam and the diagonal brace connecting beam, and form the entire supporting steel platform structure;

[0023] S5, complete the installation of beam formwork on the supporting steel platform structure, lay the floor formwork, pour the floor concrete, and perform maintenance. During this period, set a monitoring point at the end of the cantilever beam of the supporting steel platform structure to monitor the deformation degree of the cantilever beam to ensure that the deformation does not exceed the stability requirements;

[0024] S6, after the Nth layer structure construction is completed and the concrete strength reaches 100% of the design value, the cantilever steel platform is removed. First, the formwork support is removed, and then the cantilever beam connecting beam and the diagonal bracing connecting beam are removed in sections, and then the double-layer support frame and the single-layer support frame are removed.

[0025] The step S2 also includes the following specific steps:

[0026] S21, calculate the load above the supporting steel platform structure. According to the scaffolding calculation results, convert the column load to the main beam load, convert the external scaffolding load to the side beam, convert the cantilever beam to the main beam, and convert the construction board surface to the main beam to obtain the load above each main cantilever beam;

[0027] S22, analyze the elements of load action in the supporting steel platform structure and find various load combinations of dead load, live load and wind load;

[0028] S23, calculate the design value and standard value of the maximum support reaction force under each load combination at each node of the supporting steel platform, and find the most unfavorable internal force;

[0029] S24, verify the strength of each unit of the supporting steel platform, the overall stability parameters around the 2nd axis, the overall stability parameters around the 3rd axis, the shear stress ratio along the 2nd axis, the shear stress ratio along the 3rd axis, the slenderness ratio around the 2nd axis, and the slenderness ratio around the 3rd axis to determine whether the stability requirements are met.

[0030] The step S4 also includes the following specific operation sequence:

[0031] Install the short cantilever steel beam first, then the long cantilever beam;

[0032] Embedded parts are set when pouring the N-3 floor slab; embedded parts are set when pouring of the N-2 floor slab is completed; after the concrete strength of the N-2 floor slab reaches more than 50%, the N-2 support platform structure is installed, and after the construction of the N-1 main structure is completed and the concrete strength reaches more than 50%, the N-1 support platform structure is installed; after the cantilever beams and diagonal braces are fixed, the diagonal brace connecting rods and cantilever beam connecting rods are installed; the spacing between the surface layer cantilever beam tie rods is 900mm. After installation and fixation, the span is fully welded and sealed with 4mm patterned steel plates.

[0033] The single-layer cantilever steel triangular truss formwork platform and the parallel truss diagonal brace formwork platform in the prior art have the following disadvantages: (1) the diagonal brace transfers the load to the side beams of the building structure, and the load is concentrated, which has a great impact on the side beams of the building structure; (2) the formwork platform needs to be installed in place on the floor by a tower crane, and the diagonal brace is nearly 13 meters long, which brings great safety hazards to installation and removal.

[0034] Compared with the prior art, the present invention can achieve the following beneficial effects:

[0035] 1. The double-layer support frame is a two-layer cantilever steel truss formwork platform. The main cantilever beam and the secondary cantilever beam are fixed on the embedded steel parts of the floor slab. Each diagonal brace is connected to support in sequence, and the formwork load is evenly distributed and transferred to the N-1st floor, the N-2nd floor and the N-3rd floor side beams, effectively reducing the pressure on each steel structure.

[0036] 2. Several double-layer support frames and single-layer support frames are connected in a row through cantilever beams and diagonal brace beams to form a whole, which can be applied to various high-altitude cantilevers, including those with inclined outer edges;

[0037] 3. The manufacturing and hoisting of the supporting steel platform are combined with the pouring progress of each floor slab, and the installation and fixation are carried out layer by layer. The next layer will be carried out after the structure of one layer is stable. The construction process can be monitored to ensure safety;

[0038] 4. The entire supporting steel platform structure has little impact on the main structure of the building, the supporting steel platform has small deformation, and has sufficient local and overall stability and bearing capacity. The supporting steel platform is easy to install and dismantle, the construction progress is fast, and the project cost is low.

[0039] 5. The supporting steel platform structure provided by the present invention can not only effectively solve the construction difficulties of large cantilevered high-altitude over-limit cast-in-place beams, but also improve construction safety and reduce construction costs, providing a model for the construction of similar structures. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 It is a schematic diagram of the double-layer support frame monomer structure;

[0041] Figure 2 It is a schematic diagram of the single-layer support frame monomer structure;

[0042] Figure 3 It is a schematic diagram of the double-layer support frame joint structure;

[0043] Figure 4 It is a schematic diagram of a single-layer support frame joint structure;

[0044] Figure 5 This is a schematic plan view of layer N-1 of the embodiment;

[0045] Figure 6 This is a schematic plan view of layer N-2 of the embodiment;

[0046] Figure 7 This is a schematic plan view of layer N-3 of the embodiment;

[0047] Figure 8 This is a schematic diagram of the connection between the I-type steel plate embedded parts and the steel structure;

[0048] Fig. 9 This is a schematic diagram of the connection between the II-type steel plate embedded parts and the steel structure;

[0049] Fig.10 This is a schematic diagram of the connection between the U-bolt embedded parts and the steel structure;

[0050] Fig.11 This is a schematic diagram of the upper semi-finished product of the double-layer support frame;

[0051] Fig.12 It is a schematic diagram of a semi-finished product of a single-layer support frame or a lower-layer semi-finished product of a double-layer support frame.

[0052] Among them: 1. Main cantilever beam; 2. First diagonal brace; 3. Second diagonal brace; 4. Third diagonal brace; 5. Fourth diagonal brace; 6. Secondary cantilever beam; 7. Fifth diagonal brace; 8. Sixth diagonal brace; 9. Vertical brace; 10. Cantilever beam connecting beam; 11. Diagonal brace connecting beam; 12. I-type steel plate embedded parts; 13. II-type steel plate embedded parts; 14. U-type bolt embedded parts; 15. N-1th layer cast-in-place floor slab; 16. N-2th layer cast-in-place floor slab; 17. N-3th layer cast-in-place floor slab. DETAILED DESCRIPTION

[0053] The technical solution of the present invention is described in detail below with reference to the accompanying drawings, and specific embodiments are provided.

[0054] See also Figure 1-6 The present invention provides a supporting steel platform structure for large cantilevered high-altitude over-limit cast-in-place beams and slabs. The supporting steel platform is a space steel structure cantilever platform composed of a plurality of single-layer support frames and a plurality of double-layer support frames connected and combined. The single-layer support frames and the double-layer support frames are used to support the cast-in-place beams and slabs of the Nth floor above. When the cantilever length of the corresponding cast-in-place beams and slabs is less than or equal to 4.5m, the following is set Figure 2 When the cantilever length of the corresponding cast-in-place beam and slab is greater than 4.5m, or when the cantilever length of the cast-in-place beam and slab is less than or equal to 4.5m but the concentrated line load of the beam and slab is greater than or equal to 20kN / m, the following shall be set: Figure 1 The double-layer support frame shown;

[0055] See also Figure 1 The double-layer support frame includes a main cantilever beam 1 installed on the N-1th layer of cast-in-place floor 15 and cantilevered out, and a secondary cantilever beam 6 installed on the N-1th layer of cast-in-place floor 15 and cantilevered out, the extended portion of the secondary cantilever beam 6 is shorter than the extended portion of the main cantilever beam 1, a first diagonal brace 2 is fixedly installed between the end of the main cantilever beam 1 and the end of the secondary cantilever beam 6, a second diagonal brace 3 is fixedly installed between the middle of the extended portion of the main cantilever beam 1 and the portion of the secondary cantilever beam 6 located at the edge of the N-1th layer of cast-in-place floor 15, and a middle portion of the first diagonal brace 2 and a middle portion of the second diagonal brace 3 are fixedly installed between the middle of the first diagonal brace 2 and the middle of the second diagonal brace 3. A third diagonal brace 4 is fixedly installed, a fourth diagonal brace 5 is fixedly installed between the second diagonal brace 3 and the side beam of the N-1st layer cast-in-place floor 15, a fifth diagonal brace 7 is fixedly installed between the end of the secondary cantilever beam 6 and the edge of the N-3rd layer cast-in-place floor 17, a sixth diagonal brace 8 is fixedly installed between the middle of the fifth diagonal brace 7 and the side beam of the N-2nd layer cast-in-place floor 16, the main cantilever beam 1 and its diagonal brace support the Nth layer cantilever cast-in-place floor upward, the secondary cantilever beam 6 and its diagonal brace support the main cantilever beam 1 and its diagonal brace upward, and the side beam of the N-3rd layer floor supports the secondary cantilever beam 6 and its diagonal brace;

[0056] See also Figure 2The single-layer support frame only includes a main cantilever beam 1 installed on the N-1th layer cast-in-place floor slab 15 and cantilevered out, as well as a fifth diagonal brace 7 and a sixth diagonal brace 8. The fifth diagonal brace 7 is fixedly installed between the end of the main cantilever beam 1 and the side beam of the N-2th layer cast-in-place floor slab 16, and the sixth diagonal brace 8 is fixedly installed between the middle of the fifth diagonal brace 7 and the side beam of the N-1th layer cast-in-place floor slab 15;

[0057] See also Figure 1-4 Several double-layer support frames and several single-layer support frames are connected in series, and cantilever beam connecting beams 10 are fixedly installed on the top of all main cantilever beams 1 and secondary cantilever beams 6, and diagonal brace connecting beams 11 are fixedly installed in the middle of all first diagonal braces 2, the middle of the second diagonal brace 3 and the middle of the fifth diagonal brace 7. The cantilever beam connecting beams 10 and the diagonal brace connecting beams 11 connect all the connected double-layer support frames and single-layer support frames into one.

[0058] See also Figure 1 and Figure 2 Since it is necessary to hoist the semi-finished product in the installation process, the lower layer of the double-layer support frame and the single-layer support frame also include a vertical support 9, which is fixedly installed between the middle of the extended part of the secondary cantilever beam 6 of the double-layer support frame and the middle of the fifth diagonal support 7, or between the middle of the extended part of the main cantilever beam 1 of the single-layer support frame and the middle of the fifth diagonal support 7.

[0059] See also Figure 1 and Figure 2 The main cantilever beam 1 and the secondary cantilever beam 6 are located above the floor and are fixed at one end by bolting through the U-bolt embedded parts 14 in the floor. The main cantilever beam 1 is welded and fixed to the I-type steel plate embedded parts 12 at the edge of the floor. The secondary cantilever beam 6 is welded and fixed to the II-type steel plate embedded parts 13 at the edge of the floor. One end of the fourth diagonal brace 5, the fifth diagonal brace 7, and the sixth diagonal brace 8 are welded and fixed to the II-type steel plate embedded parts 12 at the edge of the floor. The main cantilever beam 1, the secondary cantilever beam 6 and the connecting parts between each diagonal brace are fixed by welding.

[0060] See also Figure 8 , I-type steel plate embedded parts 12 are embedded in the floor concrete, the steel plate is exposed on the floor, and the cantilever beam I-beam supporting the steel platform is welded and fixed to the embedded steel plate;

[0061] See also Fig. 9 , II-type steel plate embedded parts 13 are embedded in the building structure concrete, the steel plate is exposed on the upper surface of the floor or the side of the building, and the cantilever beam I-beam or diagonal bracing channel steel supporting the steel platform is welded and fixed to the embedded steel plate. (a), (b) and (c) in the figure are connection methods at different angles respectively;

[0062] See also Fig.10The U-shaped structural steel bars of the U-bolt embedded parts are embedded and anchored into the structural beam slabs. Wooden wedges are tightened between the I-beams of the cantilever beams supporting the steel platform and the bolts. A steel plate is installed on the top of the U-shaped structural steel bars and locked with nuts.

[0063] A specific embodiment of the application of the technical solution of the present invention is provided below.

[0064] A certain building project has 21 floors. The maximum cantilever length of the 21st floor beam is 7.9m, the maximum beam section is 1*1.5m, and the beam surface elevation is 94.95m.

[0065] According to the Ministry of Housing and Urban-Rural Development's Construction Office Quality (2018) No. 31 "Uniform Standard for Reliability Design of Building Structures" GB50068-2018 and "Concrete Structure Engineering Construction Code" GB50666-2011, the concrete formwork support project with a concentrated line load of 20kN / m and above belongs to the scope of sub-projects with greater risks exceeding a certain scale. The maximum cross-section of the 21-story cantilever beam of this project is 1*1.5m. According to the formula concentrated line load = permanent load (self-weight of reinforced concrete + self-weight of formwork wood) × sub-item coefficient + construction uniformly distributed load × sub-item coefficient, the concentrated load is calculated to be 53.895kN / m, which is far beyond the scope of the aforementioned standards and specifications and belongs to an over-limit beam.

[0066] Since the elevation of the 21st floor cast-in-place beam and slab is 94.95m, the installation and removal of the ground-mounted or cantilevered steel pipe high-formwork scaffolding platform has great safety risks and high costs. It is necessary to build a large cantilever support steel platform, and its selection is based on the following principles: (1) floor height; (2) the 20th floor cantilever support steel platform is equal to the 21st floor cast-in-place beam and slab cantilever length 7.9m + protective scaffolding width 1.2m = 9.1m; (3) the steel brace is optimally axially compressed, that is, the steel brace is at a 45-degree angle to the horizontal plane, and according to the compression rod stability calculation formula , when the two ends of the support are hinged, μ=1; when it is cantilevered, μ=2, so the calculated length L of the steel brace is as small as possible. (4) The steel platform has a simple structure and is easy to install and dismantle. (5) According to the architectural design of this project, no tie rods can be set above the steel platform. Whether it is a steel wire rope or a steel section, it is difficult to ensure that the tie rods can bear the force at the same time. (6) The impact on the building structure is small and the deformation of the supporting steel platform is small.

[0067] The usual single-layer cantilever steel triangular truss formwork platform is only suitable for situations where the cantilever length is roughly equal to the height of the lower floor, which is difficult to meet the requirements of this project.

[0068] If a cantilever beam is used to install a diagonal brace on the N-2nd and N-3rd floors respectively, and the two parallel diagonal braces are connected and fixed to form a parallel truss diagonal brace formwork platform, its disadvantages are: (1) the diagonal brace transfers the load to the side beams of the building structure, and it is a concentrated load, which has a great impact on the side beams of the building structure; (2) this formwork platform needs to be installed in place on the floor by a tower crane, and the length of the diagonal brace is nearly 13 meters, which brings great safety hazards to installation and removal.

[0069] Therefore, the project adopted the technical solution provided by the present invention, designed and implemented a two-story cantilevered steel truss formwork platform, which transferred the formwork load more evenly to the N-1 and N-2 floor floors; this formwork platform has small deformation and is easy to install and dismantle.

[0070] See also Figure 5-7 , which are the plan views of the supporting steel platforms distributed on the N-1st, N-2nd and N-3rd floors respectively. As can be seen from the figure, the supporting steel platform structure is composed of 6 single-layer support frames and 17 double-layer support frames in a row. Single-layer support frames are set for the cast-in-place beams with a cantilever length of less than or equal to 4.5m on the right side, and double-layer support frames are set for the cast-in-place beams with a cantilever length of more than 4.5m on the left side.

[0071] The steel materials that constitute the supporting steel platform structure are all Q235B, among which the main cantilever beam specification is I40a, the secondary cantilever beam specification is I32a, the diagonal brace specification is I28a, the cantilever beam connecting beam specification is I18, the diagonal brace connecting beam specification is 18a# channel steel, and the vertical brace specification is 8# channel steel.

[0072] The raw materials of the steel structure are 12m long standard steel materials. When the total length of the main beam components exceeds 12m, the web is butt-jointed with a 45° bevel cut, the upper and lower flanges and the web are butt-welded, and 10mm steel plates are welded and reinforced on both sides to meet the strong requirements of the raw materials. The butt joint is arranged at the anchor end of the floor slab to avoid being placed at the cantilever end.

[0073] The components required for the entire supporting steel platform are as follows:

[0074]

[0075] The supporting steel platform structure of the project was constructed in the following steps:

[0076] S1. According to the structure of the cantilevered part of the building, the supporting steel platform structure is specifically designed. According to the cantilevered length of the cast-in-place beam, a single-layer support frame or a double-layer support frame is set at the corresponding position. The material, specification, length and connection position of each steel structure are designed according to the inventive design principle;

[0077] S2, establish a finite element analysis model for the designed supporting steel platform structure, perform stability simulation calculations, appropriately adjust the material, specification, length and connection position of each steel structure according to the calculation results, and repeat the simulation calculations until all units and nodes of the supporting steel platform structure meet the stability requirements;

[0078] S3, complete the assembly of the semi-finished supporting steel platform structure on the ground, see Fig.12 The semi-finished product of the single-layer support frame includes the assembled and welded main cantilever beam, the fifth diagonal brace and the vertical brace. The semi-finished product of the double-layer support frame includes the upper semi-finished product and the lower semi-finished product. Fig.11 The upper semi-finished product includes the assembled and welded main cantilever beam, the first diagonal brace, the second diagonal brace and the third diagonal brace. Fig.12 The lower semi-finished product includes the assembled and welded secondary cantilever beam, the fifth diagonal brace and the vertical brace. Since the cantilever beams and diagonal braces of the lower semi-finished product of the double-layer support frame and the single-layer support frame semi-finished product are not enclosed after assembly, the cantilever beams and diagonal braces of the cantilever frame semi-finished product are easy to deform during hoisting, and 8# channel steel vertical braces are used for fixing and reinforcement;

[0079] S4, build the floor slabs of each floor, embed the I-type steel plate embedded parts, II-type steel plate embedded parts and U-type bolt embedded parts at the designed position, hoist the semi-finished product of the supporting steel platform structure, install the fourth diagonal brace and the sixth diagonal brace that have not been installed in the semi-finished product, install, complete the welding or bolting between each steel structure and between the floor slabs, install the cantilever beam connecting beam and the diagonal brace connecting beam, and form the entire supporting steel platform structure;

[0080] S5, complete the installation of beam formwork on the supporting steel platform structure, lay the floor formwork, pour the floor concrete, and perform maintenance. During this period, set a monitoring point at the end of the cantilever beam of the supporting steel platform structure to monitor the deformation degree of the cantilever beam to ensure that the deformation does not exceed the stability requirements;

[0081] S6, after the Nth layer structure construction is completed and the concrete strength reaches 100% of the design value, the cantilever steel platform is removed. First, the formwork support is removed, and then the cantilever beam connecting beam and the diagonal bracing connecting beam are removed in sections, and then the double-layer support frame and the single-layer support frame are removed.

[0082] This project has 1 material: Q235B: elastic modulus: 2.06*105N / mm 2 ; Poisson's ratio: 0.30; Linear expansion coefficient: 1.20*10 -5 ;Mass density: 7850kg / m 3 Specific implementation step S2, according to the calculation and analysis model, the specification inspection is carried out. The inspection results show that the structure can meet the bearing capacity calculation requirements, and the maximum stress ratio is 0.89. The design verification result table is as follows (strength and overall stability are (stress / design strength)):

[0083]

[0084]

[0085]

[0086]

[0087]

[0088] The most stringent control table is as follows:

[0089] The specific implementation step S4 also includes the following specific operation sequence:

[0090] Install the short cantilever steel beam first, then the long cantilever beam; set the embedded parts when pouring the N-3 floor slab; set the embedded parts when pouring the N-2 floor slab; after the concrete strength of the N-3 floor slab reaches more than 50%, install the N-2 support platform structure, and after the main structure of the N-1 floor is completed and the concrete strength reaches more than 50%, install the N-1 support platform structure; after the cantilever beam and diagonal brace are fixed, install the diagonal brace connecting rod and cantilever beam connecting rod; the spacing between the surface layer cantilever beam tie rods is 900mm. After installation and fixation, the span is fully welded and sealed with 4mm patterned steel plates.

[0091] It should be noted that, in order to ensure safety, a formwork scaffolding is set up on the cantilever support steel platform. This embodiment is carried out according to the following procedures: after the strength of the 20th floor structural concrete reaches 75%, the 21st floor cantilever beam and slab formwork scaffolding is set up, and after the strength of the 20th floor structural concrete reaches 100%, the 21st floor beam and slab concrete is poured.

[0092] Compared with the prior art, the double-layer support frame of the present invention is a two-layer cantilever steel truss formwork platform. The main cantilever beam and the secondary cantilever beam are fixed on the embedded steel parts of the floor slab. Each diagonal brace is connected to the support in sequence, and the formwork load is distributed and transmitted to the N-1th floor, the N-2th floor and the N-3th floor side beams in a relatively even manner, effectively reducing the pressure on each steel structure. At the same time, the manufacture and hoisting of the support steel platform are combined with the pouring progress of each floor slab. The installation and fixation are carried out layer by layer. The next layer is carried out after the structure of one layer is stable. The construction process can be monitored to ensure safety. Therefore, the entire support steel platform structure of the technical solution of the present invention has little impact on the main structure of the building, the deformation of the support steel platform is small, and it has sufficient local and overall stability and bearing capacity. The support steel platform is easy to install and dismantle, the construction progress is fast, and the project cost is low. It can effectively solve the construction problems of large cantilever high-altitude over-limit cast-in-place beams.

[0093] The above description is only a preferred example of the present invention and is not any formal or substantial limitation to the present invention. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. Any equivalent changes and modifications made to the above examples based on the essential technology of the present invention should also be regarded as the protection scope of the present invention.

Claims

1. The supporting steel platform structure of large cantilevered high-altitude over-limit cast-in-place beams and slabs is characterized by: The supporting steel platform is a space steel structure cantilever platform composed of a plurality of single-layer supporting frames and a plurality of double-layer supporting frames connected in a row and combined. The single-layer supporting frames and the double-layer supporting frames are used to support the cast-in-place beams and slabs of the Nth floor above. When the cantilever length of the corresponding cast-in-place beams and slabs is less than or equal to 4.5m, a single-layer supporting frame is set. When the cantilever length of the corresponding cast-in-place beams and slabs is greater than 4.5m, or when the cantilever length of the cast-in-place beams and slabs is less than or equal to 4.5m but the concentrated line load of the beams and slabs is greater than or equal to 20kN / m, a double-layer supporting frame is set. The double-layer support frame includes a main cantilever beam installed on the N-1th layer of cast-in-place floor and cantilevered out, and a secondary cantilever beam installed on the N-2th layer of cast-in-place floor and cantilevered out, the protruding portion of the secondary cantilever beam is shorter than the protruding portion of the main cantilever beam, a first diagonal brace is fixedly installed between the end of the main cantilever beam and the end of the secondary cantilever beam, a second diagonal brace is fixedly installed between the middle of the protruding portion of the main cantilever beam and the portion of the secondary cantilever beam located at the edge of the N-2th layer of cast-in-place floor, and a middle portion of the first diagonal brace and a middle portion of the second diagonal brace are fixedly installed between the middle of the first diagonal brace and the middle of the second diagonal brace. A third diagonal brace is fixedly installed, a fourth diagonal brace is fixedly installed between the second diagonal brace and the N-1th layer cast-in-place floor edge beam, a fifth diagonal brace is fixedly installed between the end of the secondary cantilever beam and the N-3th layer cast-in-place floor edge beam, and a sixth diagonal brace is fixedly installed between the middle of the fifth diagonal brace and the N-2th layer cast-in-place floor edge beam; the main cantilever beam and its diagonal brace support the Nth layer cantilever cast-in-place floor upward, the secondary cantilever beam and its diagonal brace support the main cantilever beam and its diagonal brace upward, and the N-3th layer floor edge beam supports the secondary cantilever beam and its diagonal brace; The single-layer support frame only includes a main cantilever beam installed on the N-1th layer of cast-in-place floor and cantilevered out, as well as a fifth diagonal brace and a sixth diagonal brace, wherein the fifth diagonal brace is fixedly installed between the end of the main cantilever beam and the N-2th layer of cast-in-place floor edge beam, and the sixth diagonal brace is fixedly installed between the middle of the fifth diagonal brace and the N-1th layer of cast-in-place floor edge beam; A plurality of the double-layer support frames and a plurality of the single-layer support frames are connected in a row, and cantilever beam connecting beams are fixedly installed on the top of all the main cantilever beams and the top of the secondary cantilever beams, and diagonal brace connecting beams are fixedly installed in the middle of all the first diagonal braces, the middle of the second diagonal brace, and the middle of the fifth diagonal brace, respectively. The cantilever beam connecting beam and the diagonal brace connecting beam connect all the connected double-layer support frames and single-layer support frames into one.

2. The supporting steel platform structure of the large cantilevered high-altitude over-limit cast-in-place beam and slab according to claim 1 is characterized by: The lower layer of the double-layer support frame and the single-layer support frame also include vertical supports, which are fixedly installed between the middle of the extended part of the secondary cantilever beam of the double-layer support frame and the middle of the fifth diagonal support, or between the middle of the extended part of the main cantilever beam of the single-layer support frame and the middle of the fifth diagonal support.

3. The supporting steel platform structure of the large cantilevered high-altitude over-limit cast-in-place beam and slab according to claim 2 is characterized by: The steel materials constituting the supporting steel platform structure are all Q235B, wherein the main cantilever beam is of specification 40a, the secondary cantilever beam is of specification 32a, the diagonal braces are of specification 28a, the cantilever beam connecting beam is of specification 18, the diagonal brace connecting beam is of specification 18a# channel steel, and the vertical brace is of specification 8# channel steel.

4. The supporting steel platform structure of the large cantilevered high-altitude over-limit cast-in-place beam and slab according to claim 1 is characterized by: The main cantilever beam and the secondary cantilever beam are located above the floor slab and are bolted and fixed at one end through U-bolt embedded parts in the floor slab. The main cantilever beam is welded and fixed to the I-type steel plate embedded parts at the edge of the floor slab, and the secondary cantilever beam is welded and fixed to the II-type steel plate embedded parts at the edge of the floor slab. One end of the fourth diagonal brace, the fifth diagonal brace, and the sixth diagonal brace are welded and fixed to the II-type steel plate embedded parts at the edge of the floor slab, and the connecting parts between the main cantilever beam, the secondary cantilever beam and each diagonal brace are fixed by welding.

5. According to claim 1, the method for constructing the supporting steel platform structure of the large cantilever high-altitude over-limit cast-in-place beam and slab comprises the following steps: S1. According to the structure of the cantilevered part of the building, the supporting steel platform structure is specifically designed. According to the cantilevered length of the cast-in-place beam, a single-layer support frame or a double-layer support frame is set at the corresponding position. The material, specification, length and connection position of each steel structure are designed according to the inventive design principle; S2, establish a finite element analysis model for the designed supporting steel platform structure, perform stability simulation calculations, appropriately adjust the material, specification, length and connection position of each steel structure according to the calculation results, and repeat the simulation calculations until all units and nodes of the supporting steel platform structure meet the stability requirements; S3, complete the assembly of the semi-finished products of the supporting steel platform structure on the ground. The semi-finished products of the single-layer support frame include the assembled and welded main cantilever beam, the fifth diagonal brace and the vertical brace. The semi-finished products of the double-layer support frame include the upper semi-finished products and the lower semi-finished products. The upper semi-finished products include the assembled and welded main cantilever beam, the first diagonal brace, the second diagonal brace and the third diagonal brace. The lower semi-finished products include the assembled and welded secondary cantilever beam, the fifth diagonal brace and the vertical brace. Because the cantilever beams and diagonal braces of the lower semi-finished products of the double-layer support frame and the semi-finished products of the single-layer support frame are not enclosed after assembly, the cantilever beams and diagonal braces of the cantilever frame semi-finished products are easy to deform during hoisting, and 8# channel steel vertical braces are used for fixing and reinforcement; S4, build the floor slabs of each floor, embed the I-type steel plate embedded parts, II-type steel plate embedded parts and U-type bolt embedded parts at the designed position, hoist the semi-finished product of the supporting steel platform structure, install the fourth diagonal brace and the sixth diagonal brace that have not been installed in the semi-finished product, install, complete the welding or bolting between each steel structure and between the floor slabs, install the cantilever beam connecting beam and the diagonal brace connecting beam, and form the entire supporting steel platform structure; S5, complete the installation of beam formwork on the supporting steel platform structure, lay the floor formwork, pour the floor concrete, and perform maintenance. During this period, set a monitoring point at the end of the cantilever beam of the supporting steel platform structure to monitor the deformation degree of the cantilever beam to ensure that the deformation does not exceed the stability requirements; S6, after the construction of the Nth floor structure is completed, the cantilever steel platform is dismantled. First, the formwork support is dismantled, and then the cantilever beam connecting beam and the diagonal bracing connecting beam are dismantled in sections, and then the double-layer support frame and the single-layer support frame are dismantled.

6. According to the method for constructing a supporting steel platform structure of a large cantilevered high-altitude over-limit cast-in-place beam and slab according to claim 5, the step S2 further comprises the following specific steps: S21, calculate the load above the supporting steel platform structure. According to the scaffolding calculation results, convert the column load to the main beam load, convert the external scaffolding load to the side beam, convert the cantilever beam to the main beam, and convert the construction board surface to the main beam to obtain the load above each main cantilever beam; S22, analyze the elements of load action in the supporting steel platform structure and find various load combinations of dead load, live load and wind load; S23, calculate the design value and standard value of the maximum support reaction force under each load combination at each node of the supporting steel platform, and find the most unfavorable internal force; S24, verify the strength of each unit of the supporting steel platform, the overall stability parameters around the 2nd axis, the overall stability parameters around the 3rd axis, the shear stress ratio along the 2nd axis, the shear stress ratio along the 3rd axis, the slenderness ratio around the 2nd axis, and the slenderness ratio around the 3rd axis to determine whether the stability requirements are met.

7. According to the method for constructing a supporting steel platform structure of a large cantilevered high-altitude over-limit cast-in-place beam and slab according to claim 5, the step S4 further comprises: Install the short cantilever steel beam first, then install the long cantilever beam; set the embedded parts when pouring the N-3 floor slab; set the embedded parts when pouring the N-2 floor slab; after the concrete strength of the N-2 floor slab reaches more than 75%, install the N-2 support platform structure, and after the main structure of the N-1 floor is completed and the concrete strength reaches more than 50%, install the N-1 support platform structure; after the cantilever beam and diagonal brace are fixed, install the diagonal brace connecting rod and cantilever beam connecting rod; the spacing between the surface layer cantilever beam tie rods is 900mm. After installation and fixation, the span is fully welded and sealed with 4mm patterned steel plates.

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