A temporary support construction method for large-span post-cast belts of shallow foundation multi-story frame structures

Abstract

The present invention discloses a temporary support construction method for a large-span post-casting belt of a multi-story frame structure with a shallow foundation, including the following steps: obtaining the size of the column grid and the position of the post-casting belt, and after bearing capacity and stability verification, designing the distribution position of the temporary support small pedestal of the post-casting belt, temporary foundation columns, and temporary structural columns, and confirming the material and strength of the temporary support foundation and temporary structural columns of the post-casting belt; according to the distribution position of the temporary support structural columns of the post-casting belt, pouring an independent foundation pedestal and a temporary rectangular foundation short column with few reinforcements on the designed natural foundation or bearing layer, and the position of the post-casting belt is retained according to the designed position; the temporary support structural columns of the post-casting belt are poured synchronously with the main structure columns according to the pre-designed distribution position, and the formwork frame is removed synchronously with the main structure to complete the system conversion. The present invention can ensure that the beams and slabs on both sides of the post-casting belt are synchronously settled with the main bodies on both sides, and ensure that the ground beams and the beams and slabs of the post-casting belt above positive and negative zero are not deformed due to the deformation of the lower part.

Description

Technical Field

[0001] The invention belongs to the technical field of construction, and in particular relates to a temporary support construction method for a large-span post-cast belt of a shallow foundation multi-story frame structure. Background Art

[0002] In the prior art, the basement top slab post-casting strip formwork support system uses a quick frame (or fastener-type scaffolding) formwork to independently support it, which is retained when the structural formwork supports on both sides are removed. It can only be removed after the concrete pouring in the post-casting strip is completed and cured for 28 days to reach the designed strength. The top slab post-casting strip support system is installed, such as Figure 1 and Figure 2 As shown in the figure, the formwork frame of the post-casting belt is independently erected and painted as a warning; generally, the soil is filled and compacted first, and then the concrete cushion layer is poured, and the bracket stands on the concrete cushion layer. Although this post-casting belt support system has good integrity, only when it is not deformed or damaged, the concrete in the span where the post-casting belt is located will maintain the initial stress state when the main concrete is poured during the period from the pouring of the main body to the completion of the pouring of the post-casting belt on both sides. However, the early stage of the post-casting belt closure is usually long, and the backfill soil will sink and deform after the floor is loaded. During this period, the sinking of the backfill soil of the post-casting belt is accelerated due to the rainy season or maintenance water, resulting in deformation and sinking of the concrete cushion layer and the bracket, and in severe cases, the post-casting belt beam slab deflects and cracks. There are usually the following disadvantages: (1) a large amount of formwork and support materials are occupied for a long time; (2) daily management is difficult, and the support materials are easily damaged or even demolished by humans; (3) materials such as formwork, square wood, and top support are easy to deform, rot, rust, etc., causing the post-casting belt formwork support system to loosen. Summary of the invention

[0003] In view of the deficiencies in the prior art, the present invention provides a temporary support construction method for a large-span post-cast strip of a shallow foundation multi-story frame structure, which avoids the technical problem of deformation and cracking of the ground beam and the post-cast strip beam slab above zero due to settlement of shallow foundation backfill and deformation of steel pipe supports.

[0004] In order to achieve the above object, the technical solution of the present invention is as follows:

[0005] A temporary support construction method for a large-span post-cast belt of a shallow foundation multi-story frame structure comprises the following steps:

[0006] S1, obtain the size of the column grid and the position of the post-casting strip, design the distribution position of the temporary supporting structural columns of the post-casting strip after bearing capacity and stability verification, and confirm the material and strength of the temporary small cap, temporary foundation column and temporary structural column of the post-casting strip;

[0007] S2, according to the distribution position of the temporary supporting structural columns of the post-casting belt, cast the independent foundation pedestal and temporary rectangular foundation short columns with few reinforcement on the designed natural foundation or bearing layer, and the position of the post-casting belt shall be retained according to the designed position;

[0008] S3, the temporary supporting structural columns of the post-cast belt are cast synchronously with the main structural columns according to the pre-designed distribution positions;

[0009] S4, pour concrete at the post-casting joint. After the concrete in the post-casting joint reaches the demoulding strength, chisel out the temporary supporting structural columns of the post-casting joint.

[0010] Furthermore, in step S1, the material of the temporary supporting structural column of the post-cast strip is plain concrete.

[0011] Furthermore, in step S1, the strength of the temporary small pedestal and temporary foundation columns below the post-cast zone ground beam and the temporary supporting structural columns above the ground beam are the same as the strength of the main foundation and the beam-slab.

[0012] Furthermore, in step S2, the post-cast strip temporarily supports the structural column, which is first positioned on the independent foundation pedestal, and its position is determined to be inside the beam end, and then laid out according to the layout plan.

[0013] Furthermore, in step S3, the post-cast strip temporarily supports the structural column, and is simultaneously erected and reinforced during the erection of the structural beam, slab and column formwork; the structural column formwork is the same as the structural column, and the joints are sealed with double-sided tape; each structural column is connected to the surrounding formwork system as a whole to ensure stability; when pouring concrete, it is vibrated together with the structural column to ensure that the concrete is uniform and dense.

[0014] Furthermore, in step S4, when chiseling, first manually chisel off the column head part from the bottom of the beam, and trim the concrete surface at the bottom of the beam and slab, and use 1:3 cement mortar for leveling; use segmented ring cutting to chisel off the structural column from top to bottom.

[0015] Beneficial effect: The present invention adds a temporary independent foundation pedestal and a temporary rectangular foundation short column with few reinforcement on the designed natural foundation or bearing layer, and uses the designed temporary independent foundation pedestal to be cast synchronously with the main structure column, and the ground beam falls on the added temporary rectangular column with few reinforcement. The post-casting strip above zero and above the positive and negative zero are provided with a plain concrete rectangular column at the same section as the temporary support of the post-casting strip. After the post-casting strips of each layer are closed to meet the design requirements, the temporary structural columns are removed by cutting the bottom of the beam to achieve the purpose of system conversion; it can ensure that the beams and slabs on both sides of the post-casting strip follow the two The main body of the side settles synchronously, and ensures that the post-casting belt beam slab above the positive and negative zero of the ground beam post-casting belt will not deform due to the deformation of the lower part; there is no need to cast the concrete cushion layer of the post-casting belt support, which reduces the amount of concrete used and the occupancy of the support, is more economical, avoids the secondary structure construction from colliding with the traditional post-casting belt steel pipe support, ensures the safety of the post-casting belt structure, improves the turnover rate of steel pipes and formwork, and greatly reduces the construction cost; the post-casting belt span can be used with the traditional post-casting steel pipe support to construct the secondary structure and decoration in advance, and the secondary structure construction and decoration start synchronously with the main body of each floor. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a top view of the structure of the prior art;

[0017] Figure 2 It is a structural side view of the prior art;

[0018] Figure 3 It is a construction process flow chart of the present invention;

[0019] Figure 4 It is a top view of the structure of the present invention;

[0020] Figure 5 It is a top view of the structure of the present invention;

[0021] Figure 6 It is a structural cross-sectional view of the present invention;

[0022] Explanation of the reference numerals in the accompanying drawings: 1-temporary small pedestal at the long cantilevered end of the post-cast strip, 2-temporary short foundation column at the long cantilevered end of the post-cast strip (reinforcement can be calculated based on the foundation burial depth), 3-temporary short foundation column at the short cantilevered end of the post-cast strip (reinforcement can be calculated based on the foundation burial depth), 4-permanent structural ground beam at the long cantilevered end of the post-cast strip on the first floor, 5-temporary plain concrete structural column at the long cantilevered end of the post-cast strip on the first floor, 6-temporary plain concrete structural column at the long cantilevered end of the post-cast strip on the second floor, 7-temporary plain concrete structural column at the long cantilevered end of the post-cast strip on the third floor, 8-temporary plain concrete structural column at the long cantilevered end of the post-cast strip on the fourth floor, 9-temporary plain concrete structural column at the long cantilevered end of the post-cast strip on the fifth floor, 10-post-cast strip area, 11-area where the formwork frame is not removed, 12-formwork dividing line, 13-post-cast strip, 14-channel steel support at the post-cast strip, 15-ordinary steel pipe fasteners connected to the formwork frame uprights. DETAILED DESCRIPTION

[0023] The present invention is described below with reference to specific examples. It will be appreciated by those skilled in the art that these examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention in any way.

[0024] A temporary support construction method for a large-span post-cast belt of a shallow foundation multi-story frame structure comprises the following steps:

[0025] S1, obtain the size of the column grid and the position of the post-casting strip, design the distribution position of the temporary supporting structural columns of the post-casting strip after bearing capacity and stability verification, and confirm the material and strength of the temporary small cap, temporary foundation column and temporary structural column of the post-casting strip;

[0026] S2, according to the distribution position of the temporary supporting structural columns of the post-casting belt, cast the independent foundation pedestal and temporary rectangular foundation short columns with few reinforcement on the designed natural foundation or bearing layer, and the position of the post-casting belt shall be retained according to the designed position;

[0027] S3, the temporary supporting structural columns of the post-cast belt are cast synchronously with the main structural columns according to the pre-designed distribution positions;

[0028] S4, pour concrete at the post-casting joint. After the concrete in the post-casting joint reaches the demoulding strength, chisel out the temporary supporting structural columns of the post-casting joint.

[0029] In this embodiment, the maximum column grid spacing is 7.2m×9m and 3m×7.2m, the structural layer height is 3.9m, and the post-cast strip is located at the 1 / 4 span. After bearing capacity and stability calculations, it is decided to install a 250mm×250mm plain concrete structural column at the end of the main beam that intersects the post-cast strip vertically, 200mm away from the edge of the post-cast strip, as a temporary support for the post-cast strip. The concrete strength is the same as that of the beam and slab, and C30 is used. The position of the post-cast strip is retained according to the designed position, and loading is strictly prohibited on the upper part of the post-cast strip.

[0030] In this embodiment, the construction project is a shallow foundation. The post-cast strip support column at the short cantilever is set on the permanent bearing platform and cast synchronously with the foundation column. The long cantilever post-cast strip support column cap is set on the bearing layer with the cap. The support cap is reinforced with DJ02 and the same grade of concrete. Its column is cast synchronously with the permanent column. The grade of the concrete support column concrete structure beam slab is C30.

[0031] 1. Layout plan:

[0032] A b (250mm, equivalent to the beam width) × h plain concrete support column is set at the end of the main beam intersecting with the post-cast strip for temporary support.

[0033] 2. Calculation of bearing capacity of first floor support columns:

[0034] According to the "Concrete Structure Design Code", Appendix D plain concrete structural member design calculation formula (without considering eccentric pressure):

[0035]

[0036] Support column parameters 1 (250×200mm): concrete strength grade C30, fc=14.3kN / mm2, fcc=0.85×14.3=12.2kN / mm2, e0=0,

[0037] Support column bearing capacity: Nu1 = 0.72 × 12.2 × 200 × 250 = 439.2 kN

[0038] Support column parameters 2 (250×250mm): concrete strength grade C30, fc=14.3kN / mm2, fcc=0.85×14.3=12.2kN / mm2, e0=0,

[0039] Support column bearing capacity: Nu2 = 0.822 × 12.2 × 250 × 250 = 626.8 kN

[0040] Support column parameters 3 (250×300mm): concrete strength grade C30, fc=14.3kN / mm2, fcc=0.85×14.3=12.2kN / mm2, e0=0, =0.822

[0041] Support column bearing capacity: Nu3 = 0.822 × 12.2 × 250 × 300 = 752.1 kN

[0042] Support column parameters 4 (250×350mm): concrete strength grade C30, fc=14.3kN / mm2, fcc=0.85×14.3=12.2kN / mm2, e0=0,

[0043] Support column bearing capacity: Nu4 = 0.822 × 12.2 × 250 × 350 = 877.5 kN

[0044] Support column parameters 5 (250×400mm): concrete strength grade C30, fc=14.3kN / mm2, fcc=0.85×14.3=12.2kN / mm2, e0=0,

[0045] Support column bearing capacity: Nu5 = 0.822 × 12.2 × 250 × 400 = 1002.8 kN

[0046] Calculation of first floor column load: (Wind load is not considered, the original structural design has met the requirements, and the wind load in this project has no obvious contribution to the axial force supported by the supporting column and can be ignored)

[0047] The most unfavorable working condition 1: N1 = beam and slab deadweight + live load

[0048] =[6×2.7×0.1×25×5(floor self-weight)+0.25×0.7×2.7×25×5(main beam self-weight)+0.25×0.6×6×25×5(secondary beam self-weight)+3.2×0.2×8.7×5.5×4(filler wall self-weight)]×1.35+[16.2×2×5(live load)]×1.4=897.2kN

[0049] The most unfavorable working condition 2: N2 = beam and slab deadweight + live load

[0050] =[4.8×2.7×0.1×25×5(floor self-weight)+0.25×0.7×2.7×25×5(main beam self-weight)+0.25×0.6×4.8×25×5(secondary beam self-weight)+3.2×0.2×7.5×5.5×4(filler wall self-weight)]×1.35+[13.0×2×5(live load)]×1.4+=744.5kN

[0051] After calculation: Condition 1, the first floor column should use at least 250×400mm section (Nu5) to meet the bearing capacity requirements.

[0052] Condition 2: The first-floor columns shall have a minimum cross-section of 250 × 350 mm (Nu4) to meet the bearing capacity requirements.

[0053] For temporary supporting columns on other floors, the same method can be used to calculate the cross-sectional dimensions that should be adopted.

[0054] 3. Bearing capacity of the foundation

[0055] Corrected design value of foundation bearing capacity:

[0056] f a =f ak +η b γ(b-3)+η d γ m (d-0.5)

[0057] fa=170+1×20×(2.5-0.5)=210kpa

[0058] Shallow foundation base pressure:

[0059]

[0060] Without considering the eccentric pressure, when the axial load acts:

[0061] p k ≤f a

[0062] The most unfavorable working condition 1: the bottom surface area of ​​the foundation A = 4272381mm2, the cross section can be selected as 2.5×2.5m

[0063] The most unfavorable working condition 2: the bottom surface area of ​​the foundation A = 3545238mm2, the cross section can be selected as 2×2m

[0064] 4. Deflection, cracks and bearing capacity of the floor slabs on both sides of the post-cast zone:

[0065] There are two types of three-side supported slabs that require special consideration in this project.

[0066] Category 1: The floor span is 2400mm×9000mm, which is a one-way slab with two short sides simply supported and two long sides with one end simply supported and one end free. According to the actual project, the finite element model is established by ABAQUS finite element software.

[0067] The analysis results are as follows:

[0068] (1) Floor deflection:

[0069] The maximum deflection occurs at the mid-span of the free long side, with a maximum displacement of only 0.0153 mm;

[0070] (2) Floor crack control:

[0071] The concrete of the floor is almost intact and there are no obvious cracks in the floor.

[0072] (3) Steel bar stress in floor slab:

[0073] The steel bars in the floor slab are basically still in an elastic state. Except for the steel bars at the supports, the steel bars in other parts are in a lower stress state.

[0074] Category II: The floor slab has a span of 2400mm×3000mm, is a two-way slab, has two short sides that are simply supported, and two long sides that are simply supported at one end and free at the other. This type of floor slab has a small span and does not require verification.

[0075] To sum up: the deflection, cracks and bearing capacity of the floor slabs on both sides of the post-cast strip can meet the requirements of the specifications, and its safety redundancy is still relatively high.

[0076] 2. Structural Column Design

[0077] 1) Structural column parameters:

[0078] b——Section width: rectangular section b×h=250mm×250mm 2 =62500mm 2 ;

[0079] ——Stability coefficient of plain concrete member: calculated according to Table D.2.1, l0 / b = (story height 3.9 - beam height 0.7) / 0.25 = 12.8, check Table D.2.1, take

[0080] f cc ——Design value of axial compressive strength of plain concrete: f c ×0.85=14.3×0.85=12.16N / mm 2 ; (See Table 4.1.4-1, concrete strength C30, f c Take 14.3);

[0081] h——section height: same as section width b, 250mm;

[0082] e0——The distance from the axial force application point to the center of the cross section: According to the vertical centered force, the force application point and the cross section center coincide, e0=e c =0;

[0083] 2) Bearing capacity of structural columns:

[0084]

[0085]

[0086] 3. Verification

[0087] According to the provisions of 3.2.1 Safety level of building structure and 8.2.8 Structural importance coefficient γ0 of GB 50068-2018 "Uniform Standard for Reliability Design of Building Structures". In this embodiment, the safety level is designed as Level 2, and the structural importance coefficient γ0 is 1.0. According to the provisions of 3.2.2 of GB 50009 2012 "Load Code for Building Structures". In summary, in this embodiment:

[0088] γ0=1.0;

[0089] S d max =N1=122.637kN;

[0090] R d =N=655.12kN;

[0091] Therefore γ0×S d =122.637kN×5=613.185KN<R d =655.12kN, meets the requirements.

[0092] The specific operation process of the structural column is as follows:

[0093] (1) The concrete structural column supports at the beam ends on both sides of the post-cast strip are first positioned on the cap, and the position of the concrete support column is determined to be 200 mm inside the beam end, and the layout is carried out according to the layout plan;

[0094] (2) The concrete structural column supports at the beam ends on both sides of the post-cast strip are erected and reinforced simultaneously during the erection of the structural beam, slab and column formwork;

[0095] (3) The formwork of the structural column is the same as that of the structural column, and the joints are sealed with double-sided tape; each structural column is connected to the surrounding formwork system as a whole to ensure stability; when pouring concrete, it is vibrated together with the structural column to ensure that the concrete is uniform and dense;

[0096] (4) When erecting the concrete structural column support at the beam end, the support column shall not be separated from the beam slab on both sides of the post-casting strip; after the post-casting strip meets the pouring conditions, the loose residues on the concrete section of the beam slab on both sides of the post-casting strip shall be chiseled off, and a groove shall be chiseled out in the middle of the beam slab to facilitate the installation of the water stop strip. When the strength of the post-casting strip reaches 100%, the system shall be converted and the concrete support columns on both sides of the post-casting strip shall be chiseled off;

[0097] (5) When removing, first manually cut and remove the column head from the bottom of the beam, and trim the concrete surface at the bottom of the beam slab, and use 1:3 cement mortar for leveling; use segmented cutting to remove the structural column from top to bottom, so that the broken concrete blocks are scattered within a limited range within the safety warning line to avoid safety accidents and facilitate the later cleaning of construction waste; when removing the concrete structural columns at the ends of the beams on both sides of the post-cast strip, they are manually chiseled and broken, and shall not be pushed down as a whole to avoid damaging the floor slab; the upper and lower layers of the post-cast strips are correspondingly arranged in this embodiment and shall not be misaligned. In the process of removal, the upper structural columns are removed first, and then the lower structural columns are removed; during the construction process, protective railings are arranged around the structural columns of the post-cast strip to avoid mechanical impact.

Claims

1. A temporary support construction method for a large-span post-cast belt of a shallow foundation multi-story frame structure, characterized in that: The steps include: S1, obtain the size of the column grid and the position of the post-casting strip, and after the bearing capacity and stability verification, design the distribution position of the temporary supporting structural columns of the post-casting strip, and confirm the material and strength of the temporary small cap, temporary foundation column and temporary structural column of the post-casting strip; the material of the temporary supporting structural column of the post-casting strip is plain concrete; the strength of the temporary small cap and temporary foundation column below the post-casting strip ground beam and the temporary supporting structural column above the ground beam is the same as that of the main foundation and beam slab; S2, according to the distribution position of the temporary supporting structural columns of the post-casting belt, cast the independent foundation pedestal and the temporary rectangular foundation short columns with few reinforcement on the designed natural foundation or bearing layer, and the position of the post-casting belt is retained according to the designed position; the temporary supporting structural columns of the post-casting belt are first positioned on the independent foundation pedestal, and their positions are determined to be inside the beam ends, and then the lines are laid out according to the layout plan; S3, the temporary supporting structural columns of the post-cast strips are cast synchronously with the main structural columns according to the pre-designed distribution positions; the temporary supporting structural columns of the post-cast strips are erected and reinforced at the same time during the erection of the structural beam, slab and column formwork; the structural column formwork is the same as the structural column, and the joints are sealed with double-sided tape; each structural column is connected to the surrounding formwork system as a whole to ensure stability; when pouring concrete, it is vibrated together with the structural column to ensure that the concrete is uniform and dense; S4, pour concrete at the post-casting joint. After the concrete in the post-casting joint reaches the demolding strength, chisel out the temporary supporting structural columns of the post-casting joint. When chiseling out, first manually chisel out the column head part from the bottom of the beam, and trim the concrete surface at the bottom of the beam and slab, and use 1:3 cement mortar for leveling; use segmented ring cutting to chisel out the structural columns from top to bottom.

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