CN103323276B - Method for fast detection and evaluation of cross-section characteristic of concrete bridge - Google Patents

Abstract

The invention relates to a method for quickly detecting and evaluating the degree of deviation of the section characteristics of a concrete bridge structure. (3) Use the strain gauge to test the strain increment value of each measuring point before and after loading; (4) Calculate the measured neutral axis position and bending stiffness of the concerned section; (5) Apply 1. Eccentric load, calculate the actual effective force-bearing area of the section; (6) Combine the test results in steps (4) and (5), and finally calculate the result; (7) The specific loading method of the structure can be vehicle load, external force, etc., The internal force in the test can be the difference between the two levels of load; (8) Repeat steps (3)-(6), then calculate the results separately, and finally take the average value. The invention has clear mechanics concept, simple operation, accurate and reliable results, and is easy to be grasped by engineers and technicians.

Description

Rapid detection and evaluation method of concrete bridge section properties

technical field

The invention belongs to the field of bridge and structural engineering, and in particular relates to a rapid detection and evaluation method for the section characteristics of concrete bridges.

Background technique

During the construction and operation of concrete bridges, due to factors such as construction errors, damage and deterioration of the cross-section during operation, the characteristics of the cross-section change.

At present, the commonly used methods for evaluating the deterioration or damage of concrete structure sections mainly include: (1) Appearance investigation + empirical method. This method is mainly to inspect the appearance quality of the structure with the naked eye or an instrument according to the relevant old bridge inspection and evaluation technical standards, and then calculate the parameters of the structure according to the relevant standard procedures; (2) Ultrasonic inspection method. Ultrasonic testing is a commonly used testing method in concrete structures at present. It is mainly divided into: ultrasonic-rebound comprehensive strength testing method for concrete strength testing, concrete compactness and integrity testing, concrete crack depth testing, etc.; (3) Load test method. This method is mainly based on the mechanical characteristics of the structure, applying an internal force approximately equal to the design load effect on the concerned section of the structure, and testing the strain and displacement of the structure, and calculating the calibration coefficient of the structure based on the corresponding theoretical values. When the coefficient is not greater than 1, it is safe, otherwise it is unsafe.

Contents of the invention

The technical problem to be solved by the present invention is to provide a rapid detection and evaluation method for the section characteristics of concrete bridges. The rapid detection and evaluation method provided by the present invention has a clear concept of mechanics, simple operation, accurate and reliable results, and is easy to be grasped by engineers and technicians. It can be applied to Quality identification during the construction of concrete bridges or rapid detection and assessment in the event of damage or deterioration.

The technical solution of the present invention: a method for quickly detecting and evaluating the degree of deviation of the structural section characteristics of a concrete bridge, which includes the following steps:

(1) According to the stress characteristics of the structure to be tested, select several places of the concerned section, and paste strain gauges or strain gauges on the upper and lower edges of the concerned section;

(2) Measure the size of the control section of the structure, calculate the theoretical values of relevant parameters (such as: A _theory , EI _theory , X _theory ), etc., and record the specific position of the strain gauge or strain gauge; assume that the current structure cares about the parameters of the section The deviation coefficients are α ₁ , α ₂ , α ₃ ;

(3) According to the mechanical characteristics of the structure, a bending moment effect M _j1 without axial force is applied to the concerned section, and the strain increment value of each measuring point before and after loading is tested with a strain gauge;

(4) Calculate the measured neutral axis position and bending stiffness of the concerned section according to the plane section assumption and elastic material mechanics theory: X _measured = , due to errors in the test process, it is recommended to take the average value of the measured bending stiffness ;

(5) Apply an eccentric load N _j , M _j2 to the member so that the tensile side is consistent with step (3), and use a strain gauge to test the strain increment value of each measuring point before and after loading; calculate the actual effective stress area of the section , because there will be test errors in the test process, it is recommended to take the average value of the effective force bearing area,

;

(6) Combining the test results in steps (4) and (5), finally calculate , , , to complete the detection and evaluation of the deviation degree of the concerned section characteristics;

(7) The specific loading method of the structure can be vehicle load, external force, etc. In order to improve the test accuracy and eliminate the influence of the initial value during the test, the internal force in the test can be the difference between the two levels of load, that is, N and M are respectively , , and the corresponding strain test result is also taken as ;

(8) Repeat steps (3)-(6), then calculate the geometric characteristics of each test section and the corresponding deviation coefficient, and finally take the average value to quantitatively evaluate the geometric characteristics and mechanical properties of the concerned section of the structure. characteristic.

This step is applicable to statically indeterminate structures. For hyperstatically indeterminate structures, the iterative method should be used to solve, that is, to substitute the calculated measured characteristic values of the concerned section into the stiffness matrix, and then repeat steps (3)-(5) until X _{is actually measured} , EI _{actual measurement} , and A _actual measurement converge until satisfactory, and finally calculate α ₁ , α ₂ , and α ₃ .

Beneficial effects of the present invention: the rapid detection and evaluation method provided by the present invention has a clear concept of mechanics, simple operation, accurate and reliable results, and is easy to be mastered by engineers and technicians. Rapid detection assessment.

Parameter Description

A——cross-sectional area, unit: mm ² ;

E——Elastic modulus of test structure material, unit: MPa;

I——section moment of inertia, unit: mm ⁴ ;

X—the height of the neutral axis of the section (the distance from the bottom edge of the section), unit: mm;

h——section height, unit: mm;

c _s ——the distance from the measuring point close to the upper edge of the section to the uppermost edge of the section, unit: mm;

c _x ——the distance from the measuring point close to the lower edge of the section to the lowermost edge of the section, unit: mm;

(or )——normal strain (or strain increment) at the measuring point near the upper edge of the section, unit: ;

(or )——positive strain (or strain increment) at the measuring point near the lower edge of the section, unit: ;

M _j1 (or )——Bending moment (or moment increment) of main girder under vertical load, unit .

N (or ), M _j2 (or )——the axial force (or axial force increment) and bending moment (or bending moment increment) of the main girder under the action of eccentric load, the units are: KN, .

Description of drawings

Fig. 1 is the front view of the general structure diagram of the test beam among the present invention,

Figure 2 is the left view of Figure 1,

Fig. 3 is a schematic diagram of mid-span bending moment loading in the present invention,

Fig. 4 is the mid-span eccentric load loading schematic diagram in the present invention,

Fig. 5 is the front view of the general structure diagram of the hollow plate in the present invention,

Figure 6 is a cross-sectional view of Figure 5,

Fig. 7 is a schematic diagram of loading in the present invention.

The dimensions of the drawings in the description of the drawings are all in millimeters (mm).

Detailed ways

A method for quickly detecting and evaluating the degree of deviation of the structural section properties of a concrete bridge, comprising the following steps:

(1) According to the stress characteristics of the structure to be tested, select several places of the concerned section, and paste strain gauges or strain gauges on the upper and lower edges of the concerned section;

(2) Measure the size of the control section of the structure, calculate the theoretical values of relevant parameters (such as: A _theory , EI _theory , X _theory ), etc., and record the specific position of the strain gauge or strain gauge; assume that the current structure cares about the parameters of the section The deviation coefficients are α ₁ , α ₂ , α ₃ ;

(3) According to the mechanical characteristics of the structure, a bending moment effect M _j1 without axial force is applied to the concerned section, and the strain increment value of each measuring point before and after loading is tested with a strain gauge;

(4) Calculate the measured neutral axis position and bending stiffness of the concerned section according to the plane section assumption and elastic material mechanics theory: X _measured = , due to errors in the test process, it is recommended to take the average value of the measured bending stiffness ;

(5) Apply an eccentric load N _j , M _j2 to the member so that the tensile side is consistent with that in step (3), and use a strain gauge to test the strain increment value of each measuring point before and after loading; calculate the actual effective force-bearing area of the section , because there will be test errors in the test process, it is recommended to take the average value of the effective force bearing area,

;

(6) Combining the test results in steps (4) and (5), finally calculate , , , to complete the detection and evaluation of the deviation degree of the concerned section characteristics;

(7) The specific loading method of the structure can be vehicle load, external force, etc. In order to improve the test accuracy and eliminate the influence of the initial value during the test, the internal force in the test can be the difference between the two levels of load, that is, N and M are respectively , , and the corresponding strain test result is also taken as ;

(8) Repeat steps (3)-(6), then calculate the geometric characteristics of each test section and the corresponding deviation coefficient, and finally take the average value to quantitatively evaluate the geometric characteristics and mechanical properties of the concerned section of the structure. characteristic.

This step is applicable to statically indeterminate structures. For hyperstatically indeterminate structures, the iterative method should be used to solve, that is, to substitute the calculated measured characteristic values of the concerned section into the stiffness matrix, and then repeat steps (3)-(5) until X _{is actually measured} , EI _{actual measurement} , and A _actual measurement converge until satisfactory, and finally calculate α ₁ , α ₂ , and α ₃ .

The following two specific examples are used as examples to illustrate

Embodiment one

Figure 1 and Figure 2 show the general structure of the test beam of a certain part of the prestressed concrete rectangular model beam in the indoor test.

Follow these steps as needed:

1. According to the stress characteristics of the structure, select the mid-span section of the test beam, and paste strain gauges on the upper and lower edges of the mid-span section;

2. Measure the section size of the structure, combine with the design drawings, and calculate the stiffness (EI) and neutral axis height (X) of the mid-span section;

Theoretical calculation results of mid-span section properties

Area A(mm ² ) Stiffness EI (×10 ¹⁴ mm ⁴ ) Neutral axis height X(mm) 300000 8.625 50.0

3. Use a jack to load the upper edge near the mid-span section, and load in sequence according to the magnitude of the load classification. The loading diagram is shown in Figure 3.

4. According to the test results in steps (3) and (4), calculate the measured bending stiffness and neutral axis height of the structure, and calculate α ₂ , α ₃ , as shown in Table 1 below (prestressed concrete hollow slab veneer static load test):

Table 1

Load level (KN m) EI _measured (×10 ¹⁴ mm ⁴ ) X _measured (mm) 37.5 8.918 527.5 75 8.701 514.4 112.5 8.834 495.7 150 8.975 521.2 187.5 8.735 539.3 225 8.897 513.4 262.5 8.941 519.6 300 8.721 531.4 average value 8.829 520.3 Difference from design value 102.4% 104.1% the α ₂ =0.024 α ₃ =0.041

5. Apply an eccentric load to the test beam by stretching the externally prestressed steel hinge, as shown in Figure 4.

6. According to the test results in step (5), calculate the measured effective force-bearing area of the structure, and calculate the corresponding parameter α ₁ , as shown in Table 2 (eccentric load test results):

Table 2

Embodiment two

Figure 5 and Figure 6 show the general structural diagram of the hollow slab for the single beam static load test of a 13-meter prestressed concrete hollow slab bridge of a certain class of highway.

Follow these steps as needed:

1. According to the stress characteristics of the structure, select the mid-span section of the hollow slab, and paste strain gauges on the upper and lower edges of the mid-span section;

2. Measure the section size of the structure, combine with the design drawings, and calculate the stiffness (EI) and the neutral axis height (X) of the mid-span section, as shown in Table 3 (theoretical calculation results of the mid-span section characteristics):

table 3

Area A(mm ² ) Rigidity EI(mm ⁴ ) Neutral axis height X(mm) 485400 9.9225×10 ¹⁴ 346.2

3. According to the test site, spread a thin layer of fine sand on the top of the hollow slab, and take into account its weight, then use steel plates and sand bags on the top to load in sequence according to the size of the load classification. The loading diagram is shown in Figure 7 Show.

4. According to the test results in steps (3) and (4), calculate the measured bending stiffness and neutral axis height of the structure, and calculate α ₂ and α ₃ , as shown in Table 4 (prestressed concrete hollow slab veneer Static load test results):

Table 4

Load level (KN m) EI _measured (×10 ¹⁴ mm ⁴ ) X _measured (mm) 118.9 10.699 331.2 237.7 10.646 335.2 335.7 10.656 331.2 433.7 10.519 328.5 510.8 10.423 339.1 588 10.164 332.7 644.3 10.035 342.2 700.6 9.882 352.0 average value 10.407 336.5 Difference from design value (%) 104.6% 97.2% the α ₂ =0.046 α ₃ =-0.028

Claims (2)

1. A quick detection and evaluation method for the degree of deviation of the structural section properties of a concrete bridge, characterized in that it comprises the following steps: (1) According to the force characteristics of the structure to be tested, select several places of the structure concerned section, and paste strain gauges or strain gauges on the upper and lower edges of the structure concerned section; (2) Measure the size of the concerned section of the structure and calculate the theoretical value: A _theory , E I _theory and X _theory , and record the specific position of the strain gauge or strain gauge; assume that the deviation coefficients of each parameter of the concerned section of the current structure are α ₁ , α ₂ , α ₃ ; (3) According to the mechanical characteristics of the structure, a bending moment effect M _j1 without axial force is applied to the concerned section of the structure, and the strain increment value of each measuring point before and after loading is measured with a strain gauge; (4) Calculate the measured neutral axis position and bending stiffness of the structure concerned section according to the plane section assumption and elastic material mechanics theory: X _measured = , due to errors in the test process, the measured bending stiffness is averaged ; (5) Apply an eccentric load N, M _j2 to the structure so that the tensile side is consistent with step (3), use the strain gauge to test the strain increment value of each measuring point before and after loading; calculate the actual effective force of the concerned section of the structure Area, due to the test error in the test process, the effective force area is the average value, ; (6) Combining the test results in steps (4) and (5), finally calculate , , , to complete the detection and evaluation of the deviation degree of the structural concerned section characteristics; (7) The specific loading method of the structure is external force; (8) Repeat steps (3)-(6), then calculate the geometric characteristics of each test section and the corresponding deviation coefficient, and finally take the average value to quantitatively evaluate the geometric characteristics and mechanical properties of the concerned section of the structure. characteristic; The meaning of each parameter is as follows: A——cross-sectional area, unit: mm ² ; E——Elastic modulus of test structure material, unit: MPa; I——section moment of inertia, unit: mm ⁴ ; X—the height of the neutral axis of the section, unit: mm; h——section height, unit: mm; c _s ——the distance from the measuring point close to the upper edge of the section to the uppermost edge of the section, unit: mm; c _x ——the distance from the measuring point close to the lower edge of the section to the lowermost edge of the section, unit: mm; ——Normal strain at the measuring point close to the upper edge of the section, unit: ; ——Normal strain at the measuring point near the lower edge of the section, unit: ; M _j1 ——bending moment of main beam under vertical load, unit ; N——Axial force of main beam under eccentric load, unit KN; M _j2 ——Bending moment of main beam under eccentric load, unit . 2. a kind of concrete bridge structure section property deviation degree quick detection evaluation method according to claim 1, it is characterized in that this method step is applicable to statically indeterminate structure, should adopt iterative method to solve for super statically indeterminate structure, be about to calculate out Substituting the measured characteristic values of the concerned section of the structure into the stiffness matrix, and then repeating steps (3)-(5) until X _measured , E The calculation results of I _{actual measurement} and A _{actual measurement} converge until satisfactory, and finally calculate α ₁ , α ₂ , and α ₃ .