A comprehensive test method for existing internal forces of components under load-holding state

Abstract

The present invention discloses a comprehensive test method for the existing internal force of a component under a load-holding state, comprising the following steps: selecting a small number of experimental vertical components, using a surface stress test method to obtain the internal force N of the vertical component; 0 , and then the vertical member internal force N is obtained by pile cutting weighing method 1 , calculate the comprehensive correction coefficient λ = ∑N 1 / ∑N 0 ; For the remaining vertical components, the surface stress test method is used to measure N 0 , and multiply it by the comprehensive correction coefficient λ to obtain the final vertical member internal force N 1 =λN 0 Except for a very small number of experimental vertical components, this method can complete the load-bearing test without truncation, which is simple, easy and accurate; load-bearing corrections can be made in special cases to further improve the test accuracy.

Description

Technical Field

[0001] The invention relates to the technical field of building measurement, and in particular to a comprehensive bearing capacity testing method for vertical components of existing buildings. Background Art

[0002] When an existing building tilts beyond the standard, it is necessary to correct the deviation and reinforce the building. For high-rise buildings with pile foundations, the pile cutting method is often used for forced landing and correction. A large number of engineering examples have shown that the stress differences of the original pile foundations of buildings with excessive tilt are large. The current pile cutting technology is to cut piles at random intervals. When the axial force of the cut pile is originally small, the additional load of the adjacent piles is small after the cut pile is cut, and it is difficult to settle, and it is difficult for the building to effectively tilt back; when the axial force of the cut pile is large, and the axial force of the adjacent piles is also large, the truncation may cause the axial force of the adjacent piles to suddenly increase and the pile head to be damaged, causing safety risks.

[0003] In terms of superstructure reconstruction, the original load-bearing walls and residences need to be demolished due to the needs of the building's use function. In order to ensure the reliability of the reinforcement, it is also necessary to test its actual internal force.

[0004] In terms of upper structure reinforcement, since the concrete strength of some wall columns is too low, which significantly affects the safe use of the structure, in order to ensure the safety of the subsequent use of the building, it is necessary to partially demolish it and replace the concrete. Before demolition, it is necessary to test its current actual stress condition.

[0005] Current technology is more focused on theoretical calculation and simulation. It is difficult to accurately test the actual stress conditions of the component with current testing methods. Summary of the invention

[0006] In view of this, the present invention provides a comprehensive testing method for the internal forces of vertical components of existing buildings, which can realize the axial force test of the pile body before pile cutting, provide data support for the specific pile cutting position and pile cutting sequence, ensure the safe and smooth progress of the correction work, and is also suitable for vertical components such as columns and walls.

[0007] The present invention provides a method for comprehensive testing of the existing internal forces of components under a load-holding state, comprising the following steps:

[0008] Select a small number of experimental vertical components and use the surface stress test method to test the internal force of the vertical components: install stress sensors on the surface of the existing vertical components under stress, cut the surface concrete around the sensors, read the sensor readings before and after cutting, and calculate the internal force N of the vertical components. 0i , where i∈[1,m], m is the number of experimental vertical components;

[0009] The internal force test of vertical components is carried out by pile cutting and weighing method: a reaction cap is set for the experimental vertical component below the surface concrete, a jack is installed between the reaction cap and the surface concrete around the component, the jack is controlled to load to the threshold value, the component is cut off, and the jack load N at this time is read. 1i ;

[0010] Calculate the comprehensive correction coefficient λ = ∑N 1i / ∑N 0i ;

[0011] For the remaining vertical members, the surface stress gauge test method is used to measure the internal force N0 of each vertical member, and multiply it by the comprehensive correction coefficient λ to obtain the final internal force N1=λN0 of each vertical member.

[0012] Furthermore, the number of experimental vertical components is m=3, or selected in proportion according to the total number of vertical components.

[0013] Furthermore, the step of testing the internal force of the vertical component using the surface stress test method specifically includes:

[0014] Stress sensors are installed on the surface of the component, and the surface stress test strain is ε0;

[0015] Cut a V-shaped groove or rectangular groove along the periphery of the sensor, at which point the strain gauge test strain is ε;

[0016] Calculate the internal force N0 of the vertical member according to different cutting methods;

[0017] in,

[0018] When the member is not tilted or defective and is in an axial compression state, the two-side notching method is used to calculate the internal force N0 value of the vertical member by the following formula:

[0019] N0=ζ1(ε-ε0)EA

[0020] ζ1=(1+μ 2 )

[0021] Where ζ1 is the stress correction coefficient of the two-sided notching method, μ is the Poisson's ratio, E is the elastic modulus of the concrete component, and A is the cross-sectional area of ​​the component;

[0022] When using a vibrating wire sensor to test surface stress, the three-sided notching method is used to calculate the internal force N0 value of the vertical member using the following formula:

[0023] N0=ζ2(ε-ε0)EA

[0024] Where, ζ2 is the stress correction coefficient of the three-side grooving method;

[0025] The four-side notching method is applicable to tests in various situations. The internal force N0 value of the vertical member can be obtained by the following formula:

[0026] N0=ζ3(ε-ε0)EA

[0027] Where ζ3 is the stress correction coefficient of the four-sided grooving method.

[0028] Furthermore, the stress correction coefficient ζ2 of the three-side grooving method is 1.1-1.2; the stress correction coefficient ζ3 of the four-side grooving method is 1.0-1.1.

[0029] Furthermore, the threshold value of the jack loading is taken as 0.8N. 0i .

[0030] Furthermore, the above method also includes the step of correcting the internal force of the vertical member under special circumstances, including:

[0031] For components with inclined foundations, the vertical component internal force N1 is corrected to N1 / cosθ according to the inclination angle θ;

[0032] For the component foundation in the eccentric compression state, the internal force of the vertical component includes axial force and bending moment. Multiple stress sensors are arranged along the surface of the component, and the axial force N0 of the vertical component is measured as:

[0033]

[0034] M=N0e

[0035] Where M is the bending moment borne by the vertical member, ε i1 is the strain of the ith sensor after cutting, ε i0 is the strain of the ith sensor before cutting, n is the number of sensors, e is the eccentricity, and it is calculated according to the stress change of each measuring point.

[0036] Furthermore, the vertical components include one or more of piles, columns and walls.

[0037] Compared with the prior art, the beneficial effects of the present invention are: ① except for a very small number of test piles, it is possible to carry out internal force testing of vertical components before cutting the piles; ② the comprehensive correction coefficient is obtained by combining the surface stress meter method and the pile body cutoff method, and the method is simple and easy with high accuracy; ③ the internal force of the vertical component is corrected under special circumstances to further improve the test accuracy; ④ it is suitable for various vertical components such as piles, columns, walls, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a schematic diagram of the surface stress test method;

[0039] Figure 2 It is a schematic diagram of the groove section in the surface stress test;

[0040] Figure 3 This is a schematic diagram of the two-sided grooving test method;

[0041] Figure 4 The change of stress state before and after grooving on both sides;

[0042] Figure 5 This is a schematic diagram of the three-side grooving test method;

[0043] Figure 6 The change of stress state before and after three-side grooving;

[0044] Figure 7 This is a schematic diagram of the four-side grooving test method;

[0045] Figure 8 The change of stress state before and after four-side grooving;

[0046] Fig. 9 This is an illustration of the pile-cut weighing method;

[0047] Fig.10 Schematic diagram of internal force test of vertical components with inclined foundation;

[0048] Fig.11 It is a schematic diagram of arranging multiple stress sensors along the pile body and stress distribution;

[0049] Fig.12 The figure is an exemplary flow chart of the vertical member internal force test according to the present disclosure. DETAILED DESCRIPTION

[0050] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0051] The present invention provides a method for testing the bearing capacity of vertical components of existing buildings, which can be applied to various vertical components such as piles, columns, walls, etc. The main process is as follows: Fig.12 shown.

[0052] Taking the comprehensive axial force test of the pile of an existing building as an example, the method provided by the present disclosure is further explained. When a vertical member is under axial compression, the internal force it bears is the axial force.

[0053] The specific steps include:

[0054] Step S1, select a small number of test piles, take 3 piles as an example, first use the surface stress test method to test the pile body axial force, install a stress sensor on the existing pile foundation under stress, cut the surface concrete around the sensor, read the sensor readings before and after the grooving and convert them into the pile body axial force N 01 , N 02 , N 03 ;

[0055] Step S2, using the pile cut weighing method to test the pile axial force, setting a reaction force cap for the pile, and using a hydraulic control system to load the jack to a threshold value (preferably 0.8N) 0i ), cut off the pile and read the jack load N at this time 11 , N 12 , N 13 ;

[0056] Step S3, according to the test pile test results, take the comprehensive correction coefficient λ = ∑N 1i / ∑N 0i , i=1,2,3;

[0057] Step S4: for all the remaining piles, the pile shaft axial force N0 is measured by the surface stress test method, and multiplied by the comprehensive correction coefficient λ, the pile shaft axial force of each pile can be obtained as N1=λN0.

[0058] Among them, in step S1, the method of obtaining the pile shaft axial force by the surface stress test method includes:

[0059] Install stress sensors on the pile body surface, cut V-shaped grooves or rectangular grooves around the sensor, and read the sensor readings before and after cutting. Figure 1 , Figure 2 The axial force of the pile body is calculated according to different cutting methods, including two-sided groove test method, three-sided groove test method and four-sided groove test method.

[0060] 1) Two-sided grooving test

[0061] When the pile body is not tilted, has no defects, and is in an axial compression state, the two-sided grooving method can be used for rapid testing. Assuming that the axial force of the pile body is N0, the strain tested by surface stress is ε0, and a portable angle grinder is used to perform two-sided grooving to see Figure 3 , so that the stress state of the cutting area changes. Figure 4 At this time, the strain gauge test strain is ε, and the pile shaft axial force N0 value can be obtained by the following formula:

[0062] N0=ζ1(ε-ε0)EA

[0063] ζ1=(1+μ 2 )

[0064] Where ζ1 is the stress correction coefficient of the two-sided grooving method, and μ is the Poisson's ratio.

[0065] 2) Three-side grooving test

[0066] When the vibrating wire sensor is used to test the surface stress, a three-sided grooving method can be used for rapid testing. Assuming that the axial force of the pile body is N0, the strain tested by the surface stress is ε0, and a portable angle grinder is used to perform three-sided grooving to see Figure 5, so that the stress state of the cutting area changes. Figure 6 (The shear stress τ in the figure is the surface stress of the test surface after grooving). At this time, the strain gauge test strain is ε. At this time, the axial force N0 value of the pile body can be obtained by the following formula:

[0067] N0=ζ2(ε-ε0)EA

[0068] In the formula, ζ2 is the stress correction coefficient of the three-sided grooving method, which is generally taken as 1.1~1.2.

[0069] 3) Four-side grooving test

[0070] In any case, the four-sided grooving method can be used for testing. Assuming that the axial force of the pile body is N0, the strain through the surface stress test is ε0, and the four-sided grooving method is used with a portable angle grinder. Figure 7 , so that the stress state of the cutting area changes. Figure 8 (The shear stress τ in the figure is the surface stress of the test surface after grooving). At this time, the strain gauge test strain is ε. At this time, the axial force N0 value of the pile body can be obtained by the following formula:

[0071] N0=ζ3(ε-ε0)EA

[0072] In the formula, ζ3 is the stress correction coefficient of the four-sided grooving method, which is generally taken as 1.0~1.1.

[0073] In step S2, the method of testing the pile body axial force by pile cutting and weighing method includes:

[0074] like Fig. 9 As shown, a reaction bull leg is set on the pile body, and the hydraulic jack is loaded by using a PLC synchronous jacking control system. After loading to 0.8N0, the pile is cut off and the pile is completely cut off, and the axial force N1 shared by the jack is read again.

[0075] According to the stress-strain monitoring result N0 and the weighing result N1 of the pile unloading jack, the comprehensive correction coefficient λ can be calculated, λ=N1 / N0.

[0076] Preferably, the above method further comprises the step of correcting the pile shaft axial force under special circumstances:

[0077] 1) Correction of inclined pile foundation angle

[0078] like Fig.10 As shown in the figure, when the pile foundation is tilted and the tilt angle is θ, the pile axial force N1 measured by the above method is corrected by angle:

[0079] N1=N1 / cosθ

[0080] 2) Correction of axial force in surface test of eccentrically compressed pile foundation

[0081] When the pile foundation is under eccentric compression, the internal forces of the vertical components include axial force and bending moment. At this time, multiple stress sensors are arranged along the surface of the pile body, such as Fig.11 As shown in the figure, the pile shaft axial force N0 is measured as:

[0082]

[0083] M=N0e

[0084] Where M is the bending moment borne by the pile, ε i1 is the strain of the ith sensor after cutting, ε i0 is the strain of the ith sensor before cutting, n is the number of sensors, e is the eccentricity, and it is calculated according to the stress change of each measuring point.

[0085] In summary, the above are only preferred embodiments of the present invention and are not intended to limit the protection scope of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A comprehensive test method for the existing internal forces of components under load, characterized in that: The following steps are involved: Select a small number of experimental vertical components and use the surface stress test method to test the internal force of the vertical components: install stress sensors on the surface of existing vertical components under stress, cut the surface concrete around the sensors, read the sensor readings before and after cutting, and calculate the internal force of the vertical components. ,in, , m is the number of experimental vertical members; The internal force test of vertical components is carried out by using the pile cutting and weighing method: a reaction cap is set for the experimental vertical component below the surface concrete, a jack is installed between the reaction cap and the surface concrete around the component, the jack is controlled to load to the threshold value, the component is cut off, and the jack load at this time is read. ; Calculate the comprehensive correction factor ; For the remaining vertical components, the internal forces of each vertical component were measured using the surface stress gauge test method. , multiplied by the comprehensive correction factor , and the final vertical member internal force is obtained ; The step of testing the internal force of a vertical component using the surface stress test method specifically includes: Stress sensors are installed on the surface of the component, and the surface stress test strain is ε0; Cut a V-shaped groove or rectangular groove along the periphery of the sensor, at which point the strain gauge test strain is ε; Calculate the internal forces of vertical components according to different cutting methods N 0; in: When the member is not tilted, has no defects, and is in an axial compression state, the two-sided notching method is used to calculate the internal force of the vertical member by the following formula: N 0 value: In the formula, is the stress correction factor of the two-side grooving method, is Poisson's ratio, E is the elastic modulus of concrete, and A is the cross-sectional area of ​​the component; When the vibrating wire sensor is used to test the surface stress, the three-side notching method is used to calculate the internal force of the vertical member by the following formula: N 0 value: In the formula, is the stress correction factor of the three-side grooving method; The four-sided notch rule is applicable to various situations. The internal force of the vertical member can be obtained by the following formula: N 0 value: In the formula, is the stress correction factor for the four-side grooving method.

2. The testing method according to claim 1, characterized in that: The number of experimental vertical components is selected in proportion to the total number of vertical components.

3. The testing method according to claim 1, characterized in that: The stress correction factor of the three-side grooving method Take 1.1~1.2; Stress correction factor for four-side grooving method Take 1.0~1.

1.

4. The testing method according to claim 1, characterized in that: The threshold value of jack loading is taken as 0.8 .

5. The testing method according to claim 1, characterized in that: The vertical members include one or more of piles, columns and walls.

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