Method for rapid detection and evaluation of prestressed concrete hollow slab floor of brick-concrete structure

Abstract

This invention belongs to the field of building structure safety assessment and urban renewal, specifically a rapid detection and assessment method for prestressed concrete hollow slab floor systems with brick-concrete structures. Through comprehensive dynamic screening, the first-order natural frequencies of each slab are obtained using accelerometers. Based on a modified dynamic model considering actual rotational constraint stiffness, the most unfavorable components are identified. Boundary treatment and graded static load tests are then performed on the most unfavorable components, and the overall load-bearing capacity is reliably assessed using load-displacement curves. This invention replaces traditional random sampling with a "general survey followed by detailed investigation" strategy to avoid missed safety hazards. The accuracy of dynamic testing is improved by inverting actual boundary stiffness. A single-person jump excitation method is used to achieve rapid non-destructive screening, and static load verification is performed only on a very small number of key components, significantly reducing testing costs, minimizing resident interference, and forming a comprehensive assessment system that considers both breadth and depth.

Description

Technical Field

[0001] This invention relates to the fields of building structural safety assessment and urban renewal, specifically a rapid detection and assessment method for brick-concrete prestressed concrete hollow slab floor slabs. Background Technology

[0002] In recent years, my country's urban construction has moved from a stage of large-scale incremental expansion to a new era of "urban renewal" with the upgrading and transformation of existing stock as its core.

[0003] In particular, prestressed concrete hollow slab floor systems often suffer from defects such as bottom cracks, grout spalling at slab joints, and loosening of end supports due to differences between early design specifications and current standards, coupled with environmental erosion and load effects during long-term use. These defects not only reduce the stiffness of the floor system but also seriously alter the boundary constraints of the hollow slab, directly affecting the integrity and load-bearing safety of the floor system. Therefore, accurate and rapid safety assessment of this type of floor system is a critical issue that urgently needs to be addressed in the renovation of old residential areas and urban renewal.

[0004] Currently, there are two main technical approaches to safety assessment of existing prestressed concrete hollow slab floors: static measurement and dynamic simulation. However, both approaches have some insurmountable problems.

[0005] Static load testing: Static load testing, which involves physically loading the floor slab and observing the deformation, directly reflects the stiffness performance of components under actual loads. It is currently the most intuitive and reliable method and is recognized by existing standards as the "gold standard" for judging structural performance. However, due to objective factors such as high testing costs, long cycles, significant interference to residents during loading operations, and certain risks of structural damage, static load testing in actual engineering projects can often only be conducted on a very small percentage of samples. Moreover, a core challenge of this "partial sampling" lies in the representativeness of the sample selection: In existing buildings, due to differences in construction quality, aging levels, and the complexity of the stress environment, the performance degradation of each hollow slab in the floor system often exhibits significant unevenness. If static load testing is conducted solely based on visual observation or random sampling of specimens, it is easy to miss the "shortest slab" component with the most severe stiffness degradation and the greatest safety hazards. If the most unfavorable component is not selected, even if the static load test results are qualified, it is difficult to truly guarantee the safety of the entire floor system.

[0006] Dynamic deduction: Dynamic testing methods based on natural frequency measurement have the advantages of being fast, non-destructive, and having a wide coverage, making them suitable for a "general survey" of the entire floor slab. However, existing dynamic assessment theories are mostly based on idealized simply supported or fixed-support boundary models, while the actual boundary conditions of existing brick-concrete hollow slab structures are often complex semi-rigid constraints. If the stiffness is directly inferred from dynamic parameters, the calculation model has a large error and it is difficult to give a legally valid final assessment conclusion like static load tests.

[0007] In summary, the key challenge in engineering testing is to organically combine the advantages of dynamic testing (rapid screening) with static load testing (precise qualitative verification) to accurately identify the most unfavorable components in the floor slab using comprehensive dynamic testing. This would guide the selection of static load test sites, avoid safety risks from blind sampling, and minimize testing workload and interference with building use. Summary of the Invention

[0008] To address the above problems, this invention proposes the following technical solution: a rapid detection and evaluation method for prestressed concrete hollow slab floor systems with brick-concrete structures, comprising the following steps:

[0009] Step 1: Determine the layout and joint positions of the hollow slabs in the floor slab to be tested, select representative hollow slabs as typical specimens, and smooth the surface of the mid-span measuring point of the typical specimens to facilitate subsequent work.

[0010] Step 2: Rigidly fix the accelerometer at the mid-span measuring point of the typical specimen, and connect the accelerometer to the dynamic signal acquisition device. Adjust the device parameters until the vibration signal can be stably acquired.

[0011] Step 3: Apply vertical pulse excitation to the typical specimen, collect the time history response data of the hollow plate through an accelerometer, and obtain the first-order natural frequency of the typical specimen through spectrum analysis;

[0012] Step 4: Establish a dynamic theoretical model of the hollow plate considering the rotational constraint stiffness of the support. Using the first natural frequency of the hollow plate obtained in Step 3, calculate the actual rotational constraint stiffness at the end of a typical specimen. Based on this, revise the dynamic theoretical model of the hollow plate and establish the correspondence between the first natural frequency and the actual bending stiffness of the component.

[0013] Step 5: Repeat steps 2 to 3 to obtain the measured first-order natural frequencies of the remaining hollow slabs in the floor slab and make a horizontal comparison. Based on the calculation values ​​of the modified hollow slab dynamic theoretical model in step 4, the most unfavorable component is selected.

[0014] Step 6: Perform boundary treatment on the most unfavorable component, remove the constraints of the surface layer, support brick wall and slab joint, and set up a displacement observation device to monitor the mid-span displacement;

[0015] Step 7: Apply elastic stage graded static loading to the most unfavorable component, record the mid-span displacement under each load level, and plot the load-displacement curve;

[0016] Step 8: Based on the load-displacement curve data obtained in Step 7, and combined with the dynamic screening results, evaluate the overall load-bearing capacity of the hollow slab floor.

[0017] The specific process of step 2 in the above-mentioned rapid detection and evaluation method for prestressed concrete hollow slab floor slabs with brick-concrete structure is as follows:

[0018] Step 21: Clean and polish the measuring point at the mid-span of the hollow slab, then fix a metal shim at the measuring point and attach the magnetic accelerometer to the metal shim; the dynamic signal acquisition equipment includes a dynamic signal testing and analysis system and a matching laptop computer.

[0019] The specific process of step 3 in the above-mentioned rapid detection and evaluation method for prestressed concrete hollow slab floor slabs with brick-concrete structures is as follows:

[0020] Step 31: The experimenter performs a jump excitation at the quarter point of the hollow plate, collects time history response data more than three times, obtains the spectrum curve through fast Fourier transform, reads multiple peak frequencies and takes the average value as the first natural frequency of the hollow plate.

[0021] The above-mentioned rapid detection and evaluation method for prestressed concrete hollow slab floor slabs with brick-concrete structures, specifically step 4, involves the following process:

[0022] Step 41: Simplify the hollow slab into a homogeneous Euler-Bernoulli beam with a uniform cross-section. The simplified differential equation for the free vibration of the hollow slab is:

[0023] ;

[0024] in, Design the bending stiffness of the components; Mass per unit length; This is the fourth-order partial derivative of the lateral displacement with respect to the spatial position. The internal elastic restoring force per unit length generated when a beam undergoes lateral deformation; These are the spatial coordinates along the length of the beam; Let be the lateral displacement of the beam, representing the beam's position in the middle of the beam. time, Deflection at the cross section; This is the second partial derivative of the lateral displacement with respect to time, i.e., the lateral acceleration of the cross section. This represents the inertial force generated per unit length of the beam during vibration; It is a time variable;

[0025] Step 42: Assume the Euler-Bernoulli beam with uniform cross-section in Step 31 undergoes simple harmonic motion, then The following simple harmonic motion solution is satisfied:

[0026] ;

[0027] in, These are the spatial coordinates along the length of the beam; This is the mode shape function, representing the distribution of amplitude along the beam length. It is the angular frequency; It is a time variable;

[0028] Will Substituting into the free vibration differential equation in step 41, we obtain the differential equation for the mode shape function:

[0029] ;

[0030] in, These are the spatial coordinates along the length of the beam; This is the mode shape function, which represents the distribution of amplitude along the beam length. mode shape function right The fourth derivative; Let be a frequency parameter, which satisfies the following relationship:

[0031] ;

[0032] in, It is the first-order natural frequency; Design the bending stiffness of the components; Mass per unit length;

[0033] Step 43: Solve the differential equation of the beam's transverse free vibration using the Krylov function, and write it in a form determined by the initial state parameters, i.e. The form of time:

[0034] ;

[0035] in, For frequency parameters; These are the spatial coordinates along the length of the beam; Design the bending stiffness of the components; , , , These represent the initial parameters of displacement, rotation, bending moment, and shear force at the endpoints of the hollow slab, respectively. , , , Both are Krylov functions. The initial lateral displacement of the hollow slab starting point The attenuation and transfer function; The initial section rotation angle at the starting point of the hollow slab The attenuation and transfer function; The initial internal bending moment at the starting point of the hollow slab The attenuation and transfer function; The initial section shear force at the start of the hollow slab The attenuation and transfer functions are expressed as follows:

[0036] ;

[0037] ;

[0038] ;

[0039] ;

[0040] in, For frequency parameters; These are the spatial coordinates along the length of the beam; The initial lateral displacement of the hollow slab starting point The attenuation and transfer function; The initial section rotation angle at the starting point of the hollow slab The attenuation and transfer function; The initial internal bending moment at the starting point of the hollow slab The attenuation and transfer function; The initial section shear force at the start of the hollow slab The attenuation and transfer function;

[0041] Step 44: Set the boundary conditions to have rotational constraint stiffness at both ends. The beam is elastically fixed, with zero vertical displacement at both ends, and one end point of the beam is set as the zero point. At the endpoints far from zero , Let be the length of the beam, i.e.:

[0042] ;

[0043] ;

[0044] ;

[0045] ;

[0046] in, For rotational constraint stiffness; for Displacement at time; for Bending moment at time; for The turning point at that time; for Displacement at time; for Bending moment at time; for The angle of rotation at time; to simplify the calculation process, let Solving for the frequency characteristic equation of the hollow plate considering elastic rotational constraints at both ends yields:

[0047] ;

[0048] in, , The length of the beam; For frequency parameters, and , It is the first-order natural frequency; To design the bending stiffness of the component, Mass per unit length; For rotational constraint stiffness;

[0049] Step 45: Substitute the first-order natural frequency obtained from the field measurement in Step 3 into the frequency characteristic equation of the hollow slab described in Step 44, and solve in reverse to obtain the expression for the actual rotational constraint stiffness at the end of a typical hollow slab. Using the known actual rotational constraint stiffness, the correspondence between the first-order natural frequency and the actual bending stiffness of the component can be obtained.

[0050] ;

[0051] in, , Let be the length of the beam. For frequency parameters, and , It is the first-order natural frequency; Design the bending stiffness of the components; Mass per unit length; For rotational constraint stiffness; This represents the actual bending stiffness of the component.

[0052] The above-mentioned rapid detection and evaluation method for prestressed concrete hollow slab floor slabs with brick-concrete structures, specifically step 6, involves the following process:

[0053] Step 61: Remove part of the brick wall, surface decoration layer and jointing mortar along the joints and support edges of the hollow slab to release the constraints of the joints and ends; then install displacement gauges at the bottom of the mid-span and at both supports of the most unfavorable component, and obtain the true mid-span net deflection by synchronously monitoring the mid-span displacement and support settlement.

[0054] The specific process of step 7 in the above-mentioned rapid detection and evaluation method for prestressed concrete hollow slab floor slabs with brick-concrete structures is as follows:

[0055] Step 71: Using standard red bricks or bagged sand and gravel as the loading material for graded static loading, load is applied according to the preset load levels to obtain the load-displacement curve; the actual bending stiffness of the component can be obtained by linearly averaging the load-displacement data under simply supported boundaries.

[0056] ;

[0057] in, The mid-span deflection values ​​under various load levels; For each level of line load; This refers to the actual bending stiffness of the component. Let be the length of the beam.

[0058] The specific process of step 8 in the above-mentioned rapid detection and evaluation method for prestressed concrete hollow slab floor slabs with brick-concrete structure is as follows:

[0059] Step 81: If the load-displacement curve obtained from the static load test shows a linear relationship, and the mid-span deflection under the maximum test load is less than the code limit, and no obvious abnormal decrease in the first-order natural frequency is found in the dynamic screening, then the overall load-bearing capacity of the floor slab is deemed to meet the requirements; if the first assessment shows that the overall load-bearing capacity of the floor slab does not meet the requirements, then the expanded sampling procedure is initiated: select 3 to 5 hollow slabs as alternative components according to the size of the floor slab; repeat steps 6 and 7 for static load tests on the alternative components, and conduct a second comprehensive evaluation of the floor slab based on the test data after expanded sampling. If the second comprehensive evaluation fails, it means that the entire floor slab is unqualified, and the entire floor slab does not meet the requirements in this evaluation.

[0060] The above-mentioned rapid testing and evaluation method for prestressed concrete hollow slab floor slabs in brick-concrete structures uses a typical specimen in step 1 that has no obvious structural damage and whose span and cross-sectional dimensions account for the largest proportion in the floor slab.

[0061] In the above-mentioned rapid detection and evaluation method for prestressed concrete hollow slab floor slabs with brick-concrete structure, the selection range of candidate components in step 81 covers the adjacent slabs of the original most unfavorable component, as well as the middle slab and edge slabs of the floor slab.

[0062] In the above-mentioned rapid detection and evaluation method for prestressed concrete hollow slab floor slabs with brick-concrete structure, the most unfavorable component selection method in step 5 is: a hollow slab with a value 30% lower than the calculated value of the modified hollow slab dynamic theory model or a hollow slab with the lowest measured first-order natural frequency.

[0063] The beneficial effects of this invention are as follows: First, this invention changes the traditional random sampling mode of static load testing. It first identifies the "most unfavorable component" through a comprehensive dynamic screening, and then performs static load verification on it. This "general survey first, detailed investigation later" strategy effectively avoids the problem of missing safety hazards due to insufficient sample representativeness and greatly improves the reliability of the evaluation conclusion.

[0064] Second, in view of the complex boundary conditions of hollow slabs in brick-concrete structures, this invention does not adopt the idealized assumption of simply supported or fixed support, but uses the Krylov function to invert the actual "rotational constraint stiffness". This makes the dynamic evaluation model more in line with engineering practice and solves the problem of large calculation deviation in traditional dynamic measurement methods.

[0065] Third, this invention utilizes single-person jump excitation for rapid screening, eliminating the need for large-scale vibration equipment and making operation simple and efficient. At the same time, it only conducts destructive static load tests (such as chiseling or surcharge) on a very small number of the most unfavorable components selected, minimizing damage to existing buildings and disturbance to residents while ensuring detection accuracy.

[0066] Fourth, it combines the "breadth" of dynamic testing with the "depth" of static load testing, and initiates an expanded sampling procedure when the static load test fails, forming a rigorous, complete and standardized comprehensive evaluation system. Attached Figure Description

[0067] Figure 1 This is a flowchart of the detection and evaluation method of the present invention. Detailed Implementation

[0068] The embodiments of the present invention are described in detail below.

[0069] See Figure 1 A rapid testing and evaluation method for prestressed concrete hollow slab floors with brick-concrete structure includes the following steps:

[0070] Step 1: Determine the layout and joint positions of the hollow slabs in the floor slab to be tested, select representative hollow slabs as typical specimens, and smooth the surface of the mid-span measuring point of the typical specimens to facilitate subsequent work.

[0071] The typical specimen in step 1 is a hollow slab with no obvious structural damage and the largest span and cross-sectional dimensions in the floor slab.

[0072] Step 2: Rigidly fix the accelerometer at the mid-span measuring point of the typical specimen, and connect the accelerometer to the dynamic signal acquisition device. Adjust the device parameters until the vibration signal can be stably acquired.

[0073] The specific process of step 2 is as follows:

[0074] Step 21: Clean and polish the measuring point at the mid-span of the hollow slab, then fix a metal shim at the measuring point and attach the magnetic accelerometer to the metal shim; the dynamic signal acquisition equipment includes a dynamic signal testing and analysis system and a matching laptop computer.

[0075] Step 3: Apply vertical pulse excitation to the typical specimen, collect the time history response data of the hollow plate through an accelerometer, and obtain the first-order natural frequency of the typical specimen through spectrum analysis;

[0076] The specific process of step 3 is as follows:

[0077] Step 31: The experimenter performs a jump excitation at the quarter point of the hollow plate, collects time history response data more than three times, obtains the spectrum curve through fast Fourier transform, reads multiple peak frequencies and takes the average value as the first natural frequency of the hollow plate.

[0078] Step 4: Establish a dynamic theoretical model of the hollow plate considering the rotational constraint stiffness of the support. Using the first natural frequency of the hollow plate obtained in Step 3, calculate the actual rotational constraint stiffness at the end of a typical specimen. Based on this, revise the dynamic theoretical model of the hollow plate and establish the correspondence between the first natural frequency and the actual bending stiffness of the component.

[0079] The specific process of step 4 is as follows:

[0080] Step 41: Simplify the hollow slab into a homogeneous Euler-Bernoulli beam with a uniform cross-section. The simplified differential equation for the free vibration of the hollow slab is:

[0081] ;

[0082] in, Design the bending stiffness of the components; Mass per unit length; This is the fourth-order partial derivative of the lateral displacement with respect to the spatial position. The internal elastic restoring force per unit length generated when a beam undergoes lateral deformation; These are the spatial coordinates along the length of the beam; Let be the lateral displacement of the beam, representing the beam's position in the middle of the beam. time, Deflection at the cross section; This is the second partial derivative of the lateral displacement with respect to time, i.e., the lateral acceleration of the cross section. This represents the inertial force generated per unit length of the beam during vibration; It is a time variable;

[0083] Step 42: Assume the Euler-Bernoulli beam with uniform cross-section in Step 31 undergoes simple harmonic motion, then The following simple harmonic motion solution is satisfied:

[0084] ;

[0085] in, These are the spatial coordinates along the length of the beam; This is the mode shape function, representing the distribution of amplitude along the beam length. It is the angular frequency; It is a time variable;

[0086] Will Substituting into the free vibration differential equation in step 41, we obtain the differential equation for the mode shape function:

[0087] ;

[0088] in, These are the spatial coordinates along the length of the beam; This is the mode shape function, which represents the distribution of amplitude along the beam length. mode shape function right The fourth derivative; Let be a frequency parameter, which satisfies the following relationship:

[0089] ;

[0090] in, It is the first-order natural frequency; Design the bending stiffness of the components; Mass per unit length;

[0091] Step 43: Solve the differential equation of the beam's transverse free vibration using the Krylov function, and write it in a form determined by the initial state parameters, i.e. The form of time:

[0092] ;

[0093] in, For frequency parameters; These are the spatial coordinates along the length of the beam; Design the bending stiffness of the components; , , , These represent the initial parameters of displacement, rotation, bending moment, and shear force at the endpoints of the hollow slab, respectively. , , , Both are Krylov functions. The initial lateral displacement of the hollow slab starting point The attenuation and transfer function; The initial section rotation angle at the starting point of the hollow slab The attenuation and transfer function; The initial internal bending moment at the starting point of the hollow slab The attenuation and transfer function; The initial section shear force at the start of the hollow slab The attenuation and transfer functions are respectively expressed as follows:

[0094] ;

[0095] ;

[0096] ;

[0097] ;

[0098] in, For frequency parameters; These are the spatial coordinates along the length of the beam; The initial lateral displacement of the hollow slab starting point The attenuation and transfer function; The initial section rotation angle at the starting point of the hollow slab The attenuation and transfer function; The initial internal bending moment at the starting point of the hollow slab The attenuation and transfer function; The initial section shear force at the start of the hollow slab The attenuation and transfer function;

[0099] Step 44: Set the boundary conditions to have rotational constraint stiffness at both ends. The beam is elastically fixed, with zero vertical displacement at both ends, and one end point of the beam is set as the zero point. At the endpoints far from zero , Let be the length of the beam, i.e.:

[0100] ;

[0101] ;

[0102] ;

[0103] ;

[0104] in, For rotational constraint stiffness; for Displacement at time; for Bending moment at time; for The turning point at that time; for Displacement at time; for Bending moment at time; for The angle of rotation at time; to simplify the calculation process, let Solving for the frequency characteristic equation of the hollow plate considering elastic rotational constraints at both ends yields:

[0105] ;

[0106] in, , The length of the beam; For frequency parameters, and , It is the first-order natural frequency; To design the bending stiffness of the component, Mass per unit length; For rotational constraint stiffness;

[0107] Step 45: Substitute the first-order natural frequency obtained from the field measurement in Step 3 into the frequency characteristic equation of the hollow slab described in Step 44, and solve in reverse to obtain the expression for the actual rotational constraint stiffness at the end of a typical hollow slab. Using the known actual rotational constraint stiffness, the correspondence between the first-order natural frequency and the actual bending stiffness of the component can be obtained.

[0108] ;

[0109] in, , Let be the length of the beam. For frequency parameters, and , It is the first-order natural frequency; Design the bending stiffness of the components; Mass per unit length; For rotational constraint stiffness; This represents the actual bending stiffness of the component.

[0110] Step 5: Repeat steps 2 to 3 to obtain the measured first-order natural frequencies of the remaining hollow slabs in the floor slab and make a horizontal comparison. Based on the calculation values ​​of the modified hollow slab dynamic theoretical model in step 4, the most unfavorable component is selected.

[0111] The most unfavorable component selection method in step 5 is: a hollow plate with a value 30% lower than the calculated value of the modified hollow plate dynamics theoretical model or a hollow plate with the lowest measured first-order natural frequency.

[0112] Step 6: Perform boundary treatment on the most unfavorable component, remove the constraints of the surface layer, support brick wall and slab joint, and set up a displacement observation device to monitor the mid-span displacement;

[0113] The specific process of step 6 is as follows:

[0114] Step 61: Remove part of the brick wall, surface decoration layer and jointing mortar along the joints and support edges of the hollow slab to release the constraints of the joints and ends; then install displacement gauges at the bottom of the mid-span and at both supports of the most unfavorable component, and obtain the true mid-span net deflection by synchronously monitoring the mid-span displacement and support settlement.

[0115] Step 7: Apply elastic stage-level static loading to the most unfavorable component, record the mid-span displacement under each load level, and plot the load-displacement curve.

[0116] The specific process of step 7 is as follows:

[0117] Step 71: Using standard red bricks or bagged sand and gravel as the loading material for graded static loading, load is applied according to the preset load levels to obtain the load-displacement curve; the actual bending stiffness of the component can be obtained by linearly averaging the load-displacement data under simply supported boundaries.

[0118] ;

[0119] in, The mid-span deflection values ​​under various load levels; For each level of line load; This refers to the actual bending stiffness of the component. Let be the length of the beam.

[0120] Step 8: Based on the load-displacement curve data obtained in Step 7, and combined with the dynamic screening results, evaluate the overall load-bearing capacity of the hollow slab floor.

[0121] The specific process of step 8 is as follows:

[0122] Step 81: If the load-displacement curve obtained from the static load test shows a linear relationship, and the mid-span deflection under the maximum test load is less than the code limit, and no obvious abnormal decrease in the first-order natural frequency is found in the dynamic screening, then the overall load-bearing capacity of the floor slab is deemed to meet the requirements; if the first assessment shows that the overall load-bearing capacity of the floor slab does not meet the requirements, then the expanded sampling procedure is initiated: select 3 to 5 hollow slabs as alternative components according to the size of the floor slab; repeat steps 6 and 7 for static load tests on the alternative components, and conduct a second comprehensive evaluation of the floor slab based on the test data after expanded sampling. If the second comprehensive evaluation fails, it means that the entire floor slab is unqualified, and the entire floor slab does not meet the requirements in this evaluation.

Claims

1. A rapid testing and evaluation method for prestressed concrete hollow slab floor systems with brick-concrete structures, characterized in that... Includes the following steps: Step 1: Determine the layout and joint positions of the hollow slabs in the floor slab to be tested, select representative hollow slabs as typical specimens, and smooth the surface of the mid-span measuring point of the typical specimens to facilitate subsequent work. Step 2: Rigidly fix the accelerometer at the mid-span measuring point of the typical specimen, and connect the accelerometer to the dynamic signal acquisition device. Adjust the device parameters until the vibration signal can be stably acquired. Step 3: Apply vertical pulse excitation to the typical specimen, collect the time history response data of the hollow plate through an accelerometer, and obtain the first-order natural frequency of the typical specimen through spectrum analysis; Step 4: Establish a dynamic theoretical model of the hollow plate considering the rotational constraint stiffness of the support. Using the first natural frequency of the hollow plate obtained in Step 3, calculate the actual rotational constraint stiffness at the end of a typical specimen. Based on this, revise the dynamic theoretical model of the hollow plate and establish the correspondence between the first natural frequency and the actual bending stiffness of the component. Step 5: Repeat steps 2 to 3 to obtain the measured first-order natural frequencies of the remaining hollow slabs in the floor slab and make a horizontal comparison. Based on the calculation values ​​of the modified hollow slab dynamic theoretical model in step 4, the most unfavorable component is selected. Step 6: Perform boundary treatment on the most unfavorable component, remove the constraints of the surface layer, support brick wall and slab joint, and set up a displacement observation device to monitor the mid-span displacement; Step 7: Apply elastic stage graded static loading to the most unfavorable component, record the mid-span displacement under each load level, and plot the load-displacement curve; Step 8: Based on the load-displacement curve data obtained in Step 7, and combined with the dynamic screening results, evaluate the overall load-bearing capacity of the hollow slab floor.

2. The rapid detection and evaluation method for prestressed concrete hollow slab floor systems with brick-concrete structures according to claim 1, characterized in that, The specific process of step 2 is as follows: Step 21: Clean and polish the measuring point at the mid-span of the hollow slab, then fix a metal shim at the measuring point and attach the magnetic accelerometer to the metal shim; the dynamic signal acquisition equipment includes a dynamic signal testing and analysis system and a matching laptop computer.

3. The rapid detection and evaluation method for prestressed concrete hollow slab floor systems with brick-concrete structures according to claim 2, characterized in that, The specific process of step 3 is as follows: Step 31: The experimenter performs a jump excitation at the quarter point of the hollow plate, collects time history response data more than three times, obtains the spectrum curve through fast Fourier transform, reads multiple peak frequencies and takes the average value as the first natural frequency of the hollow plate.

4. The rapid detection and evaluation method for prestressed concrete hollow slab floor systems with brick-concrete structures according to claim 3, characterized in that, The specific process of step 4 is as follows: Step 41: Simplify the hollow slab into a homogeneous Euler-Bernoulli beam with a uniform cross-section. The simplified differential equation for the free vibration of the hollow slab is: ； in, Design the bending stiffness of the components; Mass per unit length; This is the fourth-order partial derivative of the lateral displacement with respect to the spatial position. The internal elastic restoring force per unit length generated when a beam undergoes lateral deformation; These are the spatial coordinates along the beam's length. The lateral displacement of the beam represents the beam's position in the horizontal direction. time, Deflection at the cross section; This is the second partial derivative of the lateral displacement with respect to time, i.e., the lateral acceleration of the cross section. This represents the inertial force generated per unit length of the beam during vibration; It is a time variable; Step 42: Assume the Euler-Bernoulli beam with uniform cross-section in Step 31 undergoes simple harmonic motion, then The following simple harmonic motion solution is satisfied: ； in, These are the spatial coordinates along the beam's length. This is the mode shape function, representing the distribution of amplitude along the beam length. It is the angular frequency; It is a time variable; Will Substituting into the free vibration differential equation in step 41, we obtain the differential equation for the mode shape function: ； in, These are the spatial coordinates along the beam's length. This is the mode shape function, which represents the distribution of amplitude along the beam length. mode shape function right The fourth derivative; Let be a frequency parameter, which satisfies the following relationship: ； in, It is the first-order natural frequency; Design the bending stiffness of the components; Mass per unit length; Step 43: Solve the differential equation of the beam's transverse free vibration using the Krylov function, and write it in a form determined by the initial state parameters, i.e. The form of time: ； in, For frequency parameters; These are the spatial coordinates along the beam's length. Design the bending stiffness of the components; , , , These represent the initial parameters of displacement, rotation, bending moment, and shear force at the endpoints of the hollow slab, respectively. , , , Both are Krylov functions. The initial lateral displacement of the hollow slab starting point The attenuation and transfer function; The initial section rotation angle at the starting point of the hollow slab The attenuation and transfer function; The initial internal bending moment at the starting point of the hollow slab The attenuation and transfer function; The initial section shear force at the start of the hollow slab The attenuation and transfer functions are expressed as follows: ； ； ； ； in, For frequency parameters; These are the spatial coordinates along the beam's length. The initial lateral displacement of the hollow slab starting point The attenuation and transfer function; The initial section rotation angle at the starting point of the hollow slab The attenuation and transfer function; The initial internal bending moment at the starting point of the hollow slab The attenuation and transfer function; The initial section shear force at the start of the hollow slab The attenuation and transfer function; Step 44: Set the boundary conditions to have rotational constraint stiffness at both ends. The beam is elastically fixed, with zero vertical displacement at both ends, and one end point of the beam is set as the zero point. At the endpoints far from zero , Let be the length of the beam, i.e.: ； ； ； ； in, For rotational constraint stiffness; for Displacement at time; for Bending moment at time; for The turning point at that time; for Displacement at time; for Bending moment at time; for The angle of rotation at time; to simplify the calculation process, let Solving for the frequency characteristic equation of the hollow plate considering elastic rotational constraints at both ends yields: ； in, , The length of the beam; For frequency parameters, and , It is the first-order natural frequency; To design the bending stiffness of the component, Mass per unit length; For rotational constraint stiffness; Step 45: Substitute the first-order natural frequency obtained from the field measurement in Step 3 into the frequency characteristic equation of the hollow slab described in Step 44, and solve in reverse to obtain the expression for the actual rotational constraint stiffness at the end of a typical hollow slab. Using the known actual rotational constraint stiffness, the correspondence between the first-order natural frequency and the actual bending stiffness of the component can be obtained. ； in, , Let be the length of the beam. For frequency parameters, and , It is the first-order natural frequency; Design the bending stiffness of the components; Mass per unit length; For rotational constraint stiffness; This represents the actual bending stiffness of the component.

5. The rapid detection and evaluation method for prestressed concrete hollow slab floor systems with brick-concrete structures according to claim 4, characterized in that, The specific process of step 6 is as follows: Step 61: Remove part of the brick wall, surface decoration layer and jointing mortar along the joints and support edges of the hollow slab to release the constraints of the joints and ends; then install displacement gauges at the bottom of the mid-span and at both supports of the most unfavorable component, and obtain the true mid-span net deflection by synchronously monitoring the mid-span displacement and support settlement.

6. The rapid detection and evaluation method for prestressed concrete hollow slab floor systems with brick-concrete structures according to claim 5, characterized in that, The specific process of step 7 is as follows: Step 71: Using standard red bricks or bagged sand and gravel as the loading material for graded static loading, load is applied according to the preset load levels to obtain the load-displacement curve; the actual bending stiffness of the component can be obtained by linearly averaging the load-displacement data under simply supported boundaries. ； in, The mid-span deflection values ​​under various load levels; For each level of line load; This refers to the actual bending stiffness of the component. Let be the length of the beam.

7. The rapid detection and evaluation method for prestressed concrete hollow slab floor systems with brick-concrete structures according to claim 6, characterized in that, The specific process of step 8 is as follows: Step 81: If the load-displacement curve measured by the static load test is linear, and the mid-span deflection under the maximum test load is less than the limit specified in the code, and no obvious abnormal decrease in the first natural frequency is found in the dynamic screening, then the overall load-bearing capacity of the floor slab is deemed to meet the requirements. If the first assessment determines that the overall load-bearing capacity of the floor slab does not meet the requirements listed in step 81, then an expanded sampling procedure is initiated: select 3 to 5 hollow slabs as alternative components based on the size of the floor slab; repeat steps 6 and 7 for static load tests on the alternative components, and conduct a second comprehensive evaluation of the floor slab based on the test data after expanded sampling. If the second comprehensive evaluation fails, it means that the entire floor slab is unqualified, and the entire floor slab does not meet the requirements in this evaluation.

8. The rapid detection and evaluation method for prestressed concrete hollow slab floor systems with brick-concrete structures according to claim 1, characterized in that, The typical specimen in step 1 is a hollow slab with no obvious structural damage and the largest span and cross-sectional dimensions in the floor slab.

9. The rapid detection and evaluation method for prestressed concrete hollow slab floor systems with brick-concrete structures according to claim 7, characterized in that, The selection range of candidate components in step 81 covers the adjacent slabs of the original most unfavorable component, as well as the middle and edge slabs of the floor slab.

10. The rapid detection and evaluation method for prestressed concrete hollow slab floor systems with brick-concrete structures according to claim 1, characterized in that, The most unfavorable component selection method in step 5 is: a hollow plate with a value 30% lower than the calculated value of the modified hollow plate dynamics theoretical model or a hollow plate with the lowest measured first-order natural frequency.

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