A design and construction method for falling back of broken columns of pile foundation frame structure

Abstract

A design and construction method for falling back of broken columns of a pile foundation frame structure belongs to the technical field of building tilt correction. It is characterized by comprising: step a, broken column support analysis; step b, determining the upper and lower boundaries of the broken column (11); step c, forming the frame column upper section (1), the broken column (11) and the frame column upper section (4); step d, respectively chiseling and placing adjustable steel pipe supports (12) at the four corners of the broken column (11); step e, removing the broken column (11) and arranging a jack (17); step f, falling back of the broken column; step g, judging whether the current frame column has fallen back to a predetermined height, if it has fallen back to the predetermined height, the current frame column has completed falling back, otherwise it continues to fall back. Through the design and construction method for falling back of broken columns of the pile foundation frame structure, when the building tilts due to foundation soil expansion or groundwater floating, the building tilt correction is realized, which has the advantages of safety, reliability and simple operation.

Description

Technical Field

[0001] The invention discloses a broken column fallback design and construction method for a pile foundation frame structure, belonging to the technical field of building fallback. Background Art

[0002] The expansion of foundation soil or the rise of groundwater often causes the building to arch up. When the degree of the building's arching exceeds the requirements of relevant national standards and seriously affects the safety and normal use of the building, measures should be taken to lower it and strengthen it. There are two main reasons for the arching of the building:

[0003] (1) Due to some reasons of the foundation, base or the building itself, the foundation is uneven, which causes the building to settle unevenly and tilt. When a building tilts due to settlement, the commonly used correction method is to lift the settled part. For example: the technical solution disclosed in the Chinese invention patent with application number 202210980594.1, application date August 16, 2022, and patent name "A method for strengthening and reinforcing broken column nodes in building tilt correction"; the technical solution disclosed in the Chinese invention patent with application number 201910809338.4, application date August 29, 2019, and patent name "A method for correcting the tilt of a building by lifting it with an airbag"; and the technical solution disclosed in the Chinese invention patent with application number 202010817990.3, application date August 14, 2020, and patent name "A method for correcting the tilt of a building by rotating and shifting the foundation".

[0004] (2) The building arches upward due to reasons such as expansion of foundation soil or floating of groundwater, causing the building to tilt. The building tilt caused by this situation is not suitable for the above-mentioned method of lifting the building to achieve a fall back. Instead, the commonly used method is to correct the tilt by falling back. That is, by eliminating or reducing the bearing capacity of some piles, the building load is redistributed to other piles, forcing the pile foundation to settle and achieving the purpose of building falling back. Commonly used pile foundation unloading methods include pile top unloading method, pile body unloading method, pile end unloading method, pedestal unloading method, negative friction resistance method, etc. However, all of the above methods require excavation of the frame column foundation in the arch range of the building or the addition of auxiliary piles. Since the operation is carried out in a completed building, the construction is more difficult.

[0005] In addition to the above-mentioned pile foundation unloading method, the following technical solutions are also disclosed in the prior art, such as the excavation and watering method disclosed in the Chinese invention patent with application number 201610308406.5, application date May 10, 2016, and patent name "A method for correcting the tilt of a building by excavating and watering"; the excavation and tilting correction method disclosed in the Chinese invention patent with application number 201010212227.4, application date June 29, 2010, and patent name "Method for correcting the tilt of a building (structure) deep excavation"; and the pile loading and pressurization correction method, the immersion correction method, etc. However, these methods require an estimated settlement amount, and a large number of theoretical calculations are performed on the excavation amount and the watering amount. They are highly empirical, and the settlement amount of the frame column on the side of the building with smaller settlement during construction cannot be accurately controlled, making it difficult to ensure that the building inclination value after correction meets the requirements. Summary of the invention

[0006] The technical problem to be solved by the present invention is: to overcome the shortcomings of the prior art and provide a design and construction method for setting back a building due to local arching of a pile foundation frame structure caused by foundation soil expansion or groundwater buoyancy, which has the advantages of being safe, reliable and easy to operate.

[0007] The technical solution adopted by the present invention to solve the technical problem is: the broken column fallback design and construction method of the pile foundation frame structure, which is characterized by:

[0008] It includes the broken column support analysis stage and the broken column fall back construction stage.

[0009] In the broken column support analysis stage, step a, broken column support analysis, is performed;

[0010] During the construction phase of broken columns falling back, perform the following steps:

[0011] Step b, determining the upper and lower boundaries of the broken column on each upward arched frame column;

[0012] Step c, performing circular chiseling at the upper and lower boundaries of the broken column to form an upper section of the frame column, a broken column and a lower section of the frame column; a groove is formed between the upper section of the frame column, the lower section of the frame column and the broken column;

[0013] Step d, chiseling the four corners of the broken column in turn, and placing adjustable steel pipe supports at the chiseled corners;

[0014] Step e, removing the broken column and setting a jack at the center of the broken column;

[0015] Step f, cutting off all longitudinal stress-bearing steel bars between the upper section of the frame column and the lower section of the frame column, and sequentially lowering the adjustable steel pipe supports and jacks at the four corners;

[0016] Step g, determining whether the current frame column has fallen back to a predetermined height, if it has fallen back to the predetermined height, executing step h, otherwise returning to step f;

[0017] Step h, removing the built-in hydraulic jack;

[0018] Step i, connect the longitudinal force-bearing steel bars of the frame column, tie the stirrups, and pour the repair concrete.

[0019] Preferably, in step b, the lower boundary of the broken column is located 0.8m to 1.2m above the ground, and the position of the upper boundary is determined upward according to the height of the broken column.

[0020] Preferably, in step c, carbon fiber protective belts are respectively provided on the outer ring at the bottom of the upper section of the frame column and the outer ring at the top of the lower section of the frame column.

[0021] Preferably, in step d and step e, pads are provided at the upper and lower ends of the adjustable steel pipe support and the jack, respectively.

[0022] Preferably, in step i, the longitudinal force-bearing steel bars of the frame column are connected by means of an extruded sleeve, and the repair concrete uses a grouting material of a higher grade than the original frame column concrete.

[0023] Preferably, after executing step g, carbon fiber reinforcement belts are respectively arranged within a range of 1000 mm above and below the broken column.

[0024] Preferably, the adjustable steel pipe support includes a bracket, a nut and a screw, a thread is opened on the inner wall of the bracket, a nut is arranged at the upper port of the bracket, and the screw passes through the nut and the bracket at the same time; the threads of the bracket, nut and screw are all T-type threads.

[0025] Preferably, when there are multiple frame columns to be dropped, each frame column is dropped in sequence according to the distance to be dropped of each frame column. Compared with the prior art, the present invention has the following beneficial effects:

[0026] Through the broken column fallback design and construction method of the pile foundation frame structure, it is possible to fall back and correct the inclination of the building when the pile foundation frame structure is partially arched due to foundation soil expansion or groundwater buoyancy, which has the advantages of safety, reliability and simple operation.

[0027] Compared with the existing technology, the design and construction method of the broken column fallback of the pile foundation frame structure does not need to set up a supporting structure such as a supporting beam or a supporting bracket, and avoids the coordinated operation of multiple jacks. It is safe, reliable, and easy to operate, greatly reducing the difficulty of construction, improving construction efficiency, and reducing construction costs. At the same time, this technology only needs to be constructed on the first floor, which does not affect the normal use of the second floor and above, which is conducive to reducing the external impact of the repair work. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1This is a flow chart of the design and construction method for the broken column fallback of the pile foundation frame structure.

[0029] Figure 2 The broken column support analysis flow chart for the broken column fall design and construction method of the pile foundation frame structure.

[0030] Figure 3 Schematic diagram of the adjustable steel pipe support structure.

[0031] Figures 4 to 12 This is a schematic diagram of the design and construction method for the broken column fallback of the pile foundation frame structure.

[0032] Among them: 1. upper section of frame column 2, frame beam 3, chiseled area 4, lower section of frame column 5, foundation 6, pile 7, ground connecting beam 8, carbon fiber protective belt 9, longitudinal stress-bearing steel bars 10, groove 11, broken column 12, adjustable steel pipe support 13, pad 14, screw 15, nut 16, bracket 17, jack 18, stirrup 19, extrusion sleeve 20, repair concrete 21, carbon fiber reinforcement belt. DETAILED DESCRIPTION

[0033] Figures 1 to 12 The best embodiment of the present invention is shown below in conjunction with the attached Figures 1 to 12 The present invention is further described.

[0034] like Figure 1 As shown, a design and construction method for falling back of broken columns of a pile foundation frame structure (hereinafter referred to as the design and construction method) includes a broken column support analysis phase and a broken column falling back construction phase, specifically including the following steps:

[0035] Step 1001, broken column support analysis;

[0036] Combination Figure 2 Before construction, the broken column support analysis includes the following steps:

[0037] Step 1001-1, calculating the vertical load value of the frame column;

[0038] Use PKPM or Yingjianke structural design software to perform calculations and analysis to determine the load value F after the frame column arches;

[0039] Then, step 1001-2, the selection of the jack, and step 1001-3, the calculation of the adjustable steel pipe support 12 are performed simultaneously:

[0040] Step 1001-2, selection of the jack 17;

[0041] According to the vertical load value F of the frame column, select an appropriate hydraulic jack, and the safety factor of the hydraulic jack should not be less than 2.

[0042] Step 1001-3, calculation of the adjustable steel pipe support 12.

[0043] According to the falling height of the broken column and the specifications of the hydraulic jack, combined with the construction working surface, the height of the broken column is determined, and then the adjustable steel pipe support 12 is calculated.

[0044] Combination Figure 3 The adjustable steel pipe support 12 includes a cylindrical bracket 16, a nut 15 and a screw 14. The inner wall of the bracket 16 is provided with a thread. The upper end of the bracket 16 is provided with a nut 15 and a screw 14. The screw 14 passes through the nut 15 and the bracket 16 at the same time, and is threadedly connected with the nut 15 and the bracket 16 at the same time. The threads of the bracket 16, the nut 15 and the screw 14 are all T-type threads.

[0045] When calculating the adjustable steel pipe support 12, the following are specifically included:

[0046] 1) Selection of screw 14.

[0047] The screw 14 is a trapezoidal screw made of 45# carbon steel; considering the low speed, the nut 15 is made of aluminum bronze ZCuA110F3.

[0048] Working height of thread tooth: h=0.5p, where p is the thread pitch (mm).

[0049] 2) Calculation of screw 14 strength:

[0050] The screw only bears axial force when in working state:

[0051]

[0052] Among them, F Q is the lifting load (N), considering a double safety factor, F Q =2F; d1 is the thread minor diameter (mm); [σ] is the required stress of the screw (MPa), and [σ] of No. 45 carbon steel is = 355MPa.

[0053] 3) Calculation of nut 15 thread strength.

[0054] The shear strength condition of the nut 15 thread root is:

[0055] The bending strength condition of the thread root of nut 15 is:

[0056] Where D4 is the major diameter of the nut thread (mm); z is the number of thread turns; b is the root thickness of the thread (mm). For trapezoidal threads, b = 0.65p; l' is the bending arm (mm). [τ] is the allowable shear stress of the nut material (MPa). The allowable shear stress range of bronze is [τ] = 30 ~ 40MPa; [σ] b is the allowable bending stress of the nut material (MPa), and the allowable bending stress range of bronze is [σ] b =40~60MPa.

[0057] 4) Check the self-locking conditions of threaded pairs

[0058] For the self-locking requirements of the spiral, meet in is the thread lead angle:

[0059] d2 is the center diameter of the trapezoidal thread (mm), ρ v is the equivalent friction angle, ρ v =arctanf', f' is the equivalent friction coefficient of the thread pair, and the limit of the equivalent friction coefficient between steel and bronze is 0.08~0.10.

[0060] 5) Check the stability of screw 14.

[0061] Screw slenderness ratio Where, μ is the screw length coefficient. For the screw adjustable steel support, it can be simplified to one end fixed and the other end free, and μ = 2. l-the maximum working length of the screw (mm).

[0062] When λ≥85~90,

[0063] When λ≥85~90, for 45# high quality carbon steel,

[0064] Where E is the elastic modulus of the screw material (MPa). For steel, E = 2.06 × 10 5 MPa; I is the moment of inertia of the dangerous section (mm 4 ),

[0065] Stability conditions of compressed screw:

[0066] Step 1001-4, calculating the bearing capacity of the concrete support surface;

[0067] 1) Calculation of shear bearing capacity

[0068] Under the action of local load or concentrated reaction force, the shear bearing capacity of the plate without stirrups 18 or bent steel bars shall meet the following requirements: Q ≤(0.7β h f t +0.25σ pc,m )ημm h0

[0069] Among them, β h Is the cross-section height influence coefficient: when h0≤800mm, take β h =1.0; when h0≥2000mm, take β h =0.9. t is the design value of concrete axial tensile strength; σ pc,m It is the weighted average of the effective precompression stress of concrete in two directions on the perimeter of the critical surface according to the length, and its value is 1.0-3.5N / ㎜ 2 ; where σ DC，m Take it as 0 as the safety reserve of carrying capacity. m Critical section perimeter: the most unfavorable perimeter of the vertical section of the plate at a distance h0 / 2 from the periphery of the local load or concentrated reaction area; h0 is the effective height of the section, which is the smaller value of the distance from the lower section to the upper surface of the foundation and the distance from the upper section to the bottom of the structural beam after the frame column is truncated.

[0070] η=min(η1,η2),

[0071] Among them, η1 is the influence coefficient of the shape of the area of ​​action of local load or concentrated reaction force; η2 is the influence coefficient of the ratio of the critical section perimeter to the effective height of the plate section; β s is the comparison between the long side and the short side when the local load action area is a rectangle, β s It should not be greater than 4; when β s <2, take β s =2, when the area is a circle, take β s =2; a s is the influence coefficient of the plate-column structure type: for the center column, take a s =40, for the side column, take a s =30, the diagonal column is a s =20.

[0072] 2) Calculation of local compressive bearing capacity.

[0073] For concrete structural members equipped with indirect reinforcement, the cross-sectional dimensions of the local compression zone shall meet the following requirements:

[0074] F Q ≤1.35β c β1f c A n

[0075] Where: f c is the design value of concrete axial compressive strength; β c is the influence coefficient of concrete strength. When the concrete strength grade does not exceed C50, βc Take 1.0; β1 is the strength enhancement coefficient of concrete when it is locally compressed; A n A is the net area of ​​local concrete compression; l A is the local compression area of ​​concrete; b is the calculated bottom area under local compression.

[0076] Step 1002, determining the upper and lower boundaries of the broken column 11;

[0077] Combination Figure 4 , the same as the prior art, the top of the frame column to be processed is provided with a frame beam 2, the bottom of the frame column is a foundation 5, the outer periphery of the foundation 5 is a ground connecting beam 7, and the bottom of the foundation 5 is a pile 6. When determining the broken column 11 of the frame column, the lower edge line of the broken column 11 is delineated 1m above the ground of the first floor, and the upper edge position is determined according to the height of the broken column 11, and the chiseling area 3 is determined.

[0078] like Figure 5 As shown, the frame column is chiseled at the upper and lower edges according to the determined upper and lower edges of the broken column 11. When chiseling, a circular chiseling is performed at the upper and lower edges to form a groove 10, and the longitudinal stress-bearing steel bars 9 in the frame column are exposed.

[0079] After the grooves 10 at the upper and lower ends are formed on the surface of the frame column, the frame column is divided into three sections: the frame column upper section 1, the broken column 11 and the frame column lower section 4. A carbon fiber protective belt 8 with a height of 100 mm is respectively arranged at the outer circle at the bottom of the frame column upper section 1 and the outer circle at the top of the frame column lower section 4 to protect the concrete at the bottom of the frame column upper section 1 and the top of the frame column lower section 4.

[0080] Step 1003, the corners of the frame columns are cut and adjustable supporting steel pipes are placed;

[0081] like Figures 6-7 As shown, when further chiseling concrete at the four corners of the broken column 11, rectangular grooves are formed at the four corners of the broken column 11. Figure 3 The adjustable steel pipe support 12 is shown. The upper and lower ends of the adjustable steel pipe support 12 are respectively supported against the lower surface of the upper section 1 of the frame column and the upper surface of the lower section 4 of the frame column through the adjustable screw 14. When the adjustable steel pipe support 12 at the corner of the frame column is replaced, the core column at the center of the frame column is retained as a support protection measure.

[0082] In order to avoid unevenness at the chiseled area, pads 13 are placed at the upper and lower ends of the adjustable steel pipe support 12. The thickness of each pad 13 is 10 mm. By setting the pads 13, on the one hand, the upper and lower action surfaces of the adjustable steel pipe support 12 can be made level, and on the other hand, the concrete at the upper and lower surfaces of the adjustable steel pipe support 12 can be prevented from being damaged by excessive local pressure.

[0083] Step 1004, chiseling the core column of the frame column and placing the jack;

[0084] like Figure 8 As shown, the core column at the center of the broken column 11 is removed, and the upper frame column section 1 and the lower frame column section 4 are completely cut off and supported by adjustable steel pipe supports 12 at the four corners. After the necessary longitudinal force-bearing steel bars 9 are cut off, the jack 17 is placed at the center of the broken column 11, and pads 13 are respectively provided on the upper and lower surfaces of the jack 17.

[0085] Step 1005, the broken column 11 falls back;

[0086] After the jack 17 is placed in the broken column 11, the piston of the jack 17 is lifted, and the upper and lower ends of the jack 17 are respectively pressed against the lower surface of the frame column upper section 1 and the upper surface of the frame column lower section 4.

[0087] According to the height to which the frame column needs to fall back, cut off all the longitudinal stress-bearing steel bars 9, see Fig. 9 When the broken column 11 is falling back, the frame column is first supported by the jack 17, and then the adjustable steel pipe supports 12 at the four corners are adjusted, and then the jack 17 is depressurized, and the frame column is supported by the adjustable steel pipe supports 12 at the corners. This is repeated, and when performing the above falling back, the frame column falling back speed shall not be greater than 10mm / d.

[0088] Since the arch of a building requires multiple frame columns to be adjusted together, when the frame columns are lowered, the frame column with the largest arch displacement can be lowered first, and then lowered to the same elevation as the frame column with the second largest arch displacement value, and then lowered in coordination, and finally all the columns that need to be lowered are lowered to the same elevation. When lowering, one frame column must not be lowered completely before the rest of the frame columns are lowered.

[0089] Step 1006: Check whether the frame column falls back to a predetermined height;

[0090] Determine whether the frame column has fallen back to a predetermined height. If it has, execute step 1007; otherwise, return to execute step 1005.

[0091] Step 1007, remove the jack 17;

[0092] After the frame column is lowered, the jack 17 is depressurized and withdrawn from the broken column 11 , and the frame column is supported by the adjustable steel pipe supports 12 at the four corners, and the adjustable steel pipe supports 12 at the four corners are left at the broken column 11 .

[0093] Step 1008, pouring repair concrete 20;

[0094] The longitudinal reinforcement of the frame column is connected, the stirrups 18 are tied, and the repair concrete 20 is poured; Fig.10As shown, the longitudinal stress-bearing steel bars 9 cut off in step 1005 are connected by extruding sleeves 19, and the longitudinal stress-bearing steel bars 9 are connected and repaired, and then stirrups 18 are tied around the outer ring of the longitudinal stress-bearing steel bars 9, and the stirrups 18 are arranged in multiple layers along the vertical direction. Finally, the support of the casting formwork is re-cast, and the chiseled section of the frame column is repaired with a grouting material of a higher grade than the original frame column concrete, and repair concrete 20 is formed at the original broken column 11, as shown in FIG. Fig.11 shown.

[0095] Step 1009, strengthening the frame column section;

[0096] like Fig.12 As shown, a double-layer carbon fiber reinforcement tape 21 is pasted within a range of 1000 mm above and below the original broken column 11 to further strengthen the broken column 11.

[0097] The above is only a preferred embodiment of the present invention, and does not limit the present invention in other forms. Any technician familiar with the profession may use the above disclosed technical content to change or modify it into an equivalent embodiment with equivalent changes. However, any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention without departing from the technical solution of the present invention still belongs to the protection scope of the technical solution of the present invention.

Claims

1. A design and construction method for falling back of broken columns of a pile foundation frame structure, characterized in that: It includes the broken column support analysis stage and the broken column fall back construction stage. In the broken column support analysis stage, step a, broken column support analysis, is performed; During the construction phase of broken columns falling back, perform the following steps: Step b, determining the upper and lower boundaries of the broken column (11) on each of the upper arched frame columns; Step c, performing circular chiseling at the upper and lower boundaries of the broken column to form the frame column upper section (1), the broken column (11) and the frame column lower section (4); forming a groove (10) between the frame column upper section (1), the frame column lower section (4) and the broken column (11); Step d, chiseling the four corners of the broken column (11) in sequence, and placing adjustable steel pipe supports (12) at the chiseled corners; Step e, removing the broken column (11) and setting a jack (17) at the center of the broken column (11); Step f, cutting off all longitudinal stress-bearing steel bars (9) between the upper section (1) of the frame column and the lower section (4) of the frame column, and sequentially lowering the adjustable steel pipe supports (12) and jacks (17) at the four corners; Step g, determining whether the current frame column has fallen back to a predetermined height, if it has fallen back to the predetermined height, executing step h, otherwise returning to step f; Step h, removing the built-in hydraulic jack (17); Step i, connecting the longitudinal force-bearing steel bars (9) of the frame column, tying the stirrups (18), and pouring the repair concrete (20).

2. The design and construction method for falling back of broken columns of a pile foundation frame structure according to claim 1 is characterized in that: In step b, the lower boundary of the broken column (11) is located 0.8m to 1.2m above the ground, and the position of the upper boundary is determined upwards according to the height of the broken column (11).

3. The design and construction method for falling back of broken columns of pile foundation frame structure according to claim 1 is characterized by: In step c, a carbon fiber protective belt (8) is provided on the outer ring at the bottom of the upper section (1) of the frame column and the outer ring at the top of the lower section (4) of the frame column.

4. The design and construction method for falling back of broken columns of a pile foundation frame structure according to claim 1 is characterized by: In step d and step e, pads (13) are respectively provided at the upper and lower ends of the adjustable steel pipe support (12) and the jack (17).

5. The design and construction method for falling back of broken columns of pile foundation frame structure according to claim 1 is characterized by: In step i, the longitudinal stress-bearing steel bars (9) of the frame column are connected by means of an extrusion sleeve (19), and the repair concrete (20) uses a grouting material of a higher grade than the original frame column concrete.

6. The design and construction method for falling back of broken columns of a pile foundation frame structure according to claim 1 is characterized by: After executing step g, carbon fiber reinforcement strips (21) are respectively arranged within a range of 1000 mm above and below the broken column (11).

7. The design and construction method for falling back of broken columns of a pile foundation frame structure according to claim 1 or 4, characterized in that: The adjustable steel pipe support (12) comprises a bracket (16), a nut (15) and a screw rod (14); a thread is provided on the inner wall of the bracket (16); a nut (15) is provided at the upper end of the bracket (16); the screw rod (14) passes through the nut (15) and the bracket (16); the threads of the bracket (16), the nut (15) and the screw rod (14) are all T-type threads.

8. The design and construction method for falling back of broken columns of a pile foundation frame structure according to claim 1 is characterized by: When there are multiple frame columns to be dropped, each frame column is dropped in turn according to the distance to be dropped of each frame column.

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