TWI231362B - Method for measuring speed of longitudinal wave and thickness inside concrete plate by using stress wave - Google Patents

Abstract

This invention provides a method for measuring the speed of longitudinal wave and the thickness inside a concrete plate by using stress waves, including the following five main steps: (1) a spacing step; (2) a striking step; (3) a reading step for stress waves; (4) a measuring step for measuring the frequency of the thickness of plate; and (5) a computing step. This invention utilizes the reflection principle of stress waves, which passes through the entire thickness of the concrete plate to the bottom of the plate, simultaneously, measuring accurately the speed of longitudinal waves and the thickness inside the concrete plate and improving the measurement of the surface longitudinal waves of the concrete by ASTM C1383, which is currently in force to inquire into the thickness of the concrete plate resulting in the inaccuracy owing to the unevenness of the concrete. Therefore, this invention can improve the non-invasive detection technology on a civil structure and the project quality.

Description

1231362 V. Description of the invention (/) [Technical Field] The present invention relates to a method for detecting the longitudinal wave thickness and thickness of a concrete plate by using waves, waves, and waves. The invention uses stress waves to travel through the entire concrete period. The principle of reflection at the bottom of the plate can be obtained at the same time to obtain the P-wave velocity and thickness of the soil plate.

ο IX 5 1Α Printed by the Consumer Cooperatives of the Intellectual Property Bureau of the Ministry of Economic Affairs 2 [Previous technology] Newly completed concrete structures must undergo dimensional acceptance and be one of the main items specified in the contract, such as concrete for new rigid roads The thickness of the pavement, the concrete deck of the bridge, the spillway of the reservoir project, the concrete sloper, etc. are all structures that can only be touched on one side, and the method of measuring the thickness can only use the core sampling method. Measuring the length of the core sample as the basis for acceptance. This method is time-consuming and expensive and must be repaired at the core location. 'If the future wear resistance and water seepage are considered, the sampling method of core damage is not suitable. Therefore, in 1995, funded by the National Science Foundation of the United States, the non-destructive detection technology of the impact-echo method was researched to replace the current expensive and time-consuming core sampling method. Established the American Society for Testing and Materials (ASTM) standard measurement specifications (full name: ASTM C 1383 "Standard Test Method for Measuring the P-Wave Speed and one by one": …One

(Please read the precautions on the back before filling out this page) This paper size applies the Chinese National Standard (CNS) A4 specification (210 X 297 mm) A7 Printed by the Employees' Cooperatives of the Intellectual Property Bureau of the Ministry of Economic Affairs 1231362 " .... . 11 B7 V. Description of the Invention (1)

Method ”), as shown in Annex 1. The percussion echo method uses mechanical impact on the surface of the test object to generate transient stress fluctuations and introduces them into the object. The stress fluctuations include surface waves R (Rayleigh-wave , Referred to as R-wave or R-wave), longitudinal wave p (P-waVe, 5 or P wave) and shear wave S (S-wave, or S wave), as shown in Figure 1, where the surface wave system is along the object The surface diffuses outward away from the impact point, while the longitudinal and effort waves are transmitted forward in a spherical wave form. Among them, the pressure wave (P) is the fastest, followed by the shear wave (S), and the surface wave (R) is slightly slower than the shear wave. The surface wave (R) is the largest disturbance on the striking surface. Therefore, when the receiver is arranged on the 10 striking surface, the initial disturbance signal received is caused by the p-wave arrival. The largest disturbance signal received is caused by the arrival of the R wave. For the plate-like structure, when the longitudinal and shear waves meet the reflection interface, such as the bottom of the plate, they will be reflected back; when these reflected waves return When hitting the surface, surface displacement occurs. The receiver placed on the surface can monitor At this point, the 15 displacement response, if the receiver is arranged near the impact point, the detected displacement is mainly due to longitudinal waves. When the reflected wave reaches the impact surface, it will be reflected back to the interior of the plate. The stress wave excited by the impact will be transmitted back and forth between the top and bottom surfaces of the plate, as shown in Figure 2A, and the thickness vibration mode of the excited publication, as shown in Figure 2B, so that a knock of 20 is detected near the strike position. The strike response has a periodicity. Through the fast Fourier transform (fft), the frequency (f) of the strike response can be obtained. This frequency is related to the inverse of the time period required for the internal longitudinal wave of the concrete plate to go back and forth between the plate top and the plate bottom. The frequency (fT) (thickness frequency), as shown in Figure 2c, can be expressed by the following formula: ____ 4 This paper size applies to China National Standard (CNS) A4 (21G x 297)

tj !? line (Please read the precautions on the back before filling this page) (1) V. Description of the invention (3) r Cp.pla IT =-

2T In the foregoing formula (1), T is the thickness of the concrete plate;

Cp, plate is the apparent wave velocity of longitudinal waves propagating in the plate-like structure. According to the rule of thumb, this apparent wave velocity (non-actual wave velocity) is 96/0 of the actual wave velocity (Cp) in the infinite body. Therefore, formula (1) can be rewritten as the following formula (2) or (3), namely: (2)

_ 0.96G-2T or the thickness of the concrete plate (T) can be expressed by the following formula: 10 7 = 0.96-2fT (3) Figure 2A is a schematic diagram of the tap echo test of the concrete plate, in which the thickness of the concrete plate (T ), The actual version is 0.3m thick, and there is a receiver (the second receiver 22 in this figure, of course, the first receiver 21 can also be used instead). 15 Figure 3B shows the recorded displacement waveform. Figure 3C shows the Fourier transform amplitude spectrum. From the spectrum in Figure 3C, a high-amplitude spike (approximately 5.86 kHz) can be observed, and the frequency of this spike is the frequency (b) in formula (3). Please refer to FIG. 4A. The percussion echo test system is composed of three main components 20: a percussion source 10, two receivers (that is, the first receiver 21 and the second receiver 22), and a data-containing device. Portable computer for grabbing card (1213362 A7 in the picture ---------_________ V. Yingming squatting sun and moon (calling) " a ~ (Please read the precautions on the back before filling this page) (Shown) ° The test uses a steel ball with a diameter of 3mm ~ 12mm as the striking source J 0, and the first and second receivers 21 and 22 are a wide-band displacement receiver. A thin film (not shown) is used between the concrete surface just tested and the piezoelectric materials of the first and second receivers 21 and 22 to complete the circuits of the two receivers 21 and 22 and make the 52 receivers The devices 21 and 22 are tightly pressed against the concrete surface. The portable computer with data capture card can store the signal output by the receiver, and perform signal processing and analysis. Formula (3) is the basic formula of ASTM C 1383 for measuring the p-wave velocity and the thickness (T) of the mixed soil plate by the percussion echo method. The following describes the test procedures of ASTM C 1383 Method 10 ® for measuring P-wave velocity and thickness of concrete plates. Step 1: Measurement of P-wave velocity Printed by the Consumer Cooperatives of the Intellectual Property Bureau of the Ministry of Economic Affairs. Figures 4A and 4B are schematic diagrams of the P-wave velocity detection device and measured displacement waveforms, respectively, at a known distance L (0.3m ) Configure two receivers 21 and 22 (21 is the first receiver and 22 is the second receiver), and the appropriate distance A (0.15m) from the first receiver 21 on the surface of the concrete 15 plate, that is, the source of the strike 10 position, give a hit to generate a transient stress wave, make the three in a straight line, use the surface walking P wave wave obtained by the two receivers to the time difference (△ t), see Figure 4B 'and the aforementioned first and The distance L of the second receivers 21 and 22 can be calculated by using the following formula (4). C-~ 20 Ρ Δί (4) Step 2: Tap echo test chart. Figures 4C and 4D are schematic diagrams of the detection device for the tap echo detection and the measured spectrum chart, respectively. A tap is given on the concrete surface and the distance is very short. Small 6 This paper size applies the Chinese National Standard (CNS) A4 specification (21〇X 297 male ||) ----- 1231362 A7 Β7 10 15 Printed by the Intellectual Property Bureau of the Ministry of Economic Affairs and Consumer Cooperatives (20 〇 · 4Τ) Place one First-pick you up. , Leyi receiver 22, the displacement waveform detected is mainly because! > Caused by the arrival of the wave, the stress wave is transmitted back and forth on the top and bottom surfaces of the concrete plate, so a resonance frequency is generated, which is the thickness of the plate. (b) The digits measured by the second receiver 22 using the FFT technique The converted wave I is turned to the frequency 4 area to obtain the spectrum content. The high amplitude spikes in the spectrum diagram are the imported stress waves that meet the boundary of the bottom of the plate. The thickness of the plate caused by the top and bottom reflection multiple times. From the step-measured P-wave speed instead of formula (3), the thickness of the concrete plate can be obtained, that is, the plate thickness (D). It is known from the above test steps that the current thickness measurement of the concrete plate of ASTM C 1383 is measured by the surface longitudinal wave velocity (Cp) and the tap echo test measured on the surface of the concrete plate. The thickness frequency (fT) 'is then substituted into formula (3) to calculate the thickness (τ) of the concrete plate. Here is an example to explain in detail as follows, suppose the thickness (T) of the concrete version of a project is 0.2m. Figure 5A and B are top views and schematic diagrams of the measurement of the surface longitudinal wave velocity of the concrete plate by the ASTM C 1383 method, respectively. Among them, the actual plate length (L), plate width (W), and plate thickness (T) are respectively 1.2, 1.2 and 0.199m 'There are seven measuring lines on it, the distance between line a, line b and line c is 0.2m, and the distance between line D, line E, line F and line G is 0.15m. Figures 5C and D are the waveforms measured by the first receiver 21 and the second receiver 22 after tapping on the measurement line A, respectively. The time of arrival of the longitudinal waves on the surface is (ti) and ( D 't1 = -3 6.7; / s & t2 = 43.4 // s, the time difference between the two is eight 1 = 1241 = 43.4-(-36 · 7) = 80 · 1 // 8, the first and second The distance (L) between the receivers 21 and 22, L = 0.3m, and the surface P wave velocity is 3745m / s according to formula (4). The time when the longitudinal wave reaches the first receiver 21 (M is negative, this Data retrieval

(Please read the precautions on the back before filling out this page) This paper size is applicable to China National Standard (CNS) A4 (21 × X 297 mm) 1231362 Printed by the Consumer Cooperatives of the Intellectual Property Bureau of the Ministry of Economic Affairs

A7. Explanation of the invention (6) The system sets the signal to zero when the signal reaches the excitation threshold, and the effective signal generated by the tap usually occurs before the excitation. Therefore, when data is acquired, it will be set to the pre-trigger mode. Therefore, the wave-to-signal time captured by the first receiver 21 will appear at a negative value. Since only the time between q and L is required, it only needs to take the relative time difference, which does not affect the accuracy of the measurement. Then perform the tap echo test. The instrument configuration is shown in Figure 6A, and Figure 6B is the waveform measured by the second receiver 22 after the tap. The fast Fourier transform (FFT) is performed on the waveform in Figure 6B. The spectrogram shown in FIG. 60 clearly indicates that the plate thickness frequency of the tap response is 9334 Hz. The wave velocity 3745m / s and thickness frequency 9334Hz measured on the measuring line A were substituted into formula (3) to obtain a plate thickness of 0.193m and a comparison with the actual thickness of 0.2m. The measurement error was -3.5%. If the same method is used to measure the surface longitudinal wave velocities of the other six measurement lines of the concrete version according to the aforementioned ASTM c 1383 method, the obtained data and measurement errors are listed in Table 1 below, with a maximum error of 5.0 %, The average error is also 2 5%, and the accuracy is poor. Table 1 Results of measuring P-wave velocity and plate thickness by conventional methods I Applicable to China National Standard (CNS) A4 (210 X 297 mm 1231362 A7-B7 V. Description of the invention (7) 10 However, conventional methods Existing serious errors, after careful discussion, it is found that there is an obvious inconsistency here. Also, the P-wave velocity (cp) in formula 应 should be the P-wave velocity inside the concrete version, not the P-wave velocity in Table 5. Let ’s assume the same. Because concrete is a composite material composed of cement, sand, aggregate, and water, which is an inhomogeneous material, the surface P-wave velocity measured on the surface will not be consistent with the internal P-wave velocity. From the point of view, its inconsistency can sometimes be as high as 10% or more. Taking the longitudinal P-wave velocity on the surface as the P-wave velocity inside the plate will inevitably make subsequent calculations inaccurate. Therefore, if the current ASTM C is applied, such as concrete There are obvious errors between the measured wave velocity and thickness measurement method and the actual value. Therefore, this problem must be overcome. [Objective and Effect] 15 20 The main purpose of the present invention is to In order to solve the above problems, a measurement method is provided to accurately measure the internal longitudinal wave velocity and thickness of the concrete plate. The invention uses the principle of reflection of the stress wave traveling through the thickness of the entire concrete plate to the bottom of the plate, and can simultaneously measure the inside of the concrete plate P-wave velocity and thickness, but now ASTM C 1383 only measures the P-wave velocity of the concrete surface to estimate the thickness of the concrete plate. In this way, the results obtained by the present invention are closer to the actual value and the accuracy is high. It is to solve the above problems and provide a measurement method to accurately measure the internal longitudinal wave velocity and thickness of the concrete plate. The required equipment is simple, low cost, and L_1_ 9 > Paper scale 'T family standard (CNS) A4 specification ⑵G χ 297 public ^ I231362 A7 B7 V. Explain (?) 仃, so it can improve the level of non-destructive detection technology and engineering quality of civil building structures 10 15 Ministry of Economic Affairs wisdom Printed by the property bureau employee consumer cooperative [Technical content] The present invention provides a method for detecting concrete by stress waves. The method of internal P-wave velocity and thickness includes the following steps: 1. The distance setting step: Estimate the thickness (T) of the plate to be detected, prepare a first receiver and a second receiver, and determine the appropriate second receiver. The minimum distance (H) from the striking source, and the distance between the striking source and the second receiver must be greater than the minimum distance (H), where the minimum distance (该) must satisfy the following formula: ^ > 2rxtan50.5 ° 2. Step of tapping: read the origin of the tapping time (t0) of the first receiver after tapping, 3. Step of reading the stress wave: Read the longitudinal wave of the first receiver The bottom reflection reaches the door (tp), and finds the internal walking time Δίρ 求; Fourth, the thickness measurement step of the plate: Set the first or second receiver, and perform the knock echo test to obtain the plate thickness frequency (fT); V. Calculation steps: Use the following two formulas: Quantities (please read the precautions on the back before filling this page) This paper size is applicable to China National Standard (CNS) A4 (210 X 297 mm) 1231362

V. Description of the invention (Cp ⑹ (々) λ / ^ χ,) 2: 0 · 9216 and r = 096Cp

Xfi) ❼ Calculate the internal longitudinal wave velocity (Cp) inside the concrete and the thickness (τ) of the concrete soil plate. The above and other objects and advantages of the present invention can be easily understood from the detailed description and accompanying drawings of the selected embodiments below. Of course, the present invention allows some differences in the arrangement or arrangement of other parts, but the selected embodiment is described in detail in this specification and its structure is shown in the drawings. [Brief description of the diagram] Figure 1 is a schematic diagram of the various wave diffusion modes after striking. Figure 2 A is the stress wave excited by the striking and will drive back and forth between the top and bottom of the plate. 15 Figure 2 B-plate thickness vibration mode Schematic diagram 1C is the spectrum diagram of the tapping response. Fig. 3A is the diagram of the tap echo test of the concrete version. Figs. 3B and 3C are the measured displacement waveforms and spectrum diagrams. 4A and 4B are the P waves. Schematic diagram of speed detection device and displacement waveform diagram of measurement 20 Figures 4C and 4D are schematic diagrams of detection device and measurement spectrum diagram of tap echo detection, respectively. 11 This paper size applies to China National Standard (CNS) A4 specification (210 X 297 mm) (Please read the precautions on the back before filling out this page} Η ding ·; line · printed by the employee consumer cooperative of the Intellectual Property Bureau of the Ministry of Economy Version wide WP wave speed Cp 1231362 A7

V. Description of the invention (W) Figure 5A and B are top views and schematic diagrams of the configuration of measuring the surface longitudinal wave velocity and thickness of the concrete plate according to ASTM C 1383, respectively. Figures 5C and D are the waveforms measured by the two receivers. Figures 6A, 6B, and 6C are respectively the assembly drawing, measured displacement chart, and spectrum diagram of the invention's thick frequency measurement step 5. Figures 7A and 7B are experimental device diagrams and waves of the longitudinal wave reflection behavior inside the concrete, respectively. Figures 8A and 8B of the signal are the configuration diagrams and measurement results of experiments larger than the minimum distance of 055m. 10 Figures 9A, 9B, and 9C are assembly drawings of the first embodiment of the invention and Waveforms measured by the two receivers. Figures 10A, 10B, and 10C indirectly calculate the r-wave velocity measurement of the surface at the origin of the striking time. Waveforms measured by the two receivers. Figures 11A, 10 1B and 11c are the assembly diagram of the second embodiment of the present invention and the waveform diagram measured by the second receiver is shown in FIG. 12. The 12th diagram is the flowchart of the present invention. [Illustration of drawing number]

Surface wave R 20 Shear wave S version Long Y version Thick T Apparent wave speed Cp, plate P wave arrival time through plate bottom reflection t This paper size applies Chinese national standard

(Please read the precautions on the back before filling this page) I23l362 5 10 15 20 k Description of invention (丨 1) Tap the time origin t. Time measured by the first receiver tl Surface walking time difference Δt Distance between the strike source and the first receiver A Distance between the strike source and the second receiver Η The initial perturbation time of the P wave directly from L between the two receivers tps Warp Perturbation time of P wave after bottom reflection Initial perturbation time of direct S wave tsh Initial perturbation time of direct R wave tR Strike source 10 Receiver 21, 22 (21 is the first receiver; 22 is the second receiver ) Fixed distance step 51 Knock step 52 Stress wave reading step 53 Thick plate frequency measurement step 54 Calculation step 55 [Detailed description of the embodiment] The figure shown is the structure of the selected embodiment of the present invention, this is only For illustrative purposes, this structure is not restricted by patent applications. The invention is a method for detecting the internal longitudinal wave velocity and thickness of a concrete plate by a stress wave. Regarding the technical principle of the present invention, when a point impact is given to the surface of an object, a transient stress wave will be generated and introduced into the object. The stress wave includes pressure wave (p_wave) and shear wave (S_ wave). ) And surface wave (R_wave), in which pressure wave and shear wave are measured at the second receiver in the object t: internal walking time difference △ t reflection angle 0 line 13 This paper size applies Chinese National Standard (CNS) A4 specification (210 X 297 mm) 1231362 A7 V. Description of the invention (/ 2) The part is driven forward in a hemispherical waveform, while the surface wave spreads outward along the surface of the object away from the impact point, as shown in Figure 1. Among them, the pressure wave (P) has the fastest speed, the frying force wave (S) is the second, and the surface wave (R) is slightly slower than the shear wave. 5 Here please refer to Figures 7A and 7B 'These are the instrument and equipment diagrams of the longitudinal wave reflection behavior inside the concrete and the wave-to-signal pattern of the reflected wave obtained from the theoretical numerical analysis.' The reflected wave-to-signal in Figure 7B has been Disturbance signals of P-wave, S-wave and R-wave arriving along the concrete surface are removed. From this theoretical analysis, it can be known that when the incident angle and reflection angle 0 of the longitudinal wave is greater than 50.5 degrees, the reflected P wave will be reversed from a downward waveform to an upward waveform. If the reflection angle 0 is too small, then it will be measured. The signal is non-steering and less obvious, which is difficult to measure accurately. Therefore, the limiting condition of the minimum distance (H) from the striking source to the second receiver 22 can be obtained as the following formula (5) 10 15 H > 2T X tan 50.5 ° (5) 20 Assuming a plate thickness (T ) Is 0.2m. According to formula (5), it can be known that the minimum distance (H) should be greater than 0.485m. If the distance (H) is 0.55m for the experiment, the configuration diagram is shown in Figure 8A, the signal result in Figure 8b can be obtained, and the lower waveform diagram in Figure 8b is the removal of the p along the concrete surface. The disturbance signal of the arrival of waves, S waves, and R waves. The upper waveform in Figure 8B is the actual measured waveform. It will include the disturbance signals of P waves, s waves, and R waves transmitted along the concrete surface. Among them, according to the time sequence, tps is the initial perturbation time of the p wave transmitted along the surface; this paper size applies the Chinese National Standard (CNS) A4 regulations; | each (210 X 297 public) (please first (Read the notes on the back and fill out this page)

^ 31362 A7 ^^ —---- B7 —__ 5. Description of the invention ⑴) ~ ——---- ^ tpb is the perturbation time of the p wave reflected by the bottom of the plate; ish is the S wave driven along the surface The initial perturbation time is the initial perturbation time of the R wave propagating along the surface.

Γ Jing first read the precautions on the back before filling out this page) and the above tpb is the time when the reflected p wave is required by the present invention. In the following embodiments, only the tp is used to indicate the arrival time of the reflected p wave. Please refer to FIG. 12. The present invention “method for detecting the internal longitudinal wave velocity and thickness of a concrete plate by stress waves” mainly includes the following steps: a. Distance setting step 51; 10 two. Tapping step 52; three. Stress Wave reading step 5 3; 4. Plate thickness frequency measurement step 54; and 5. Calculation step 55. Here is an example of measuring the plate thickness using ASTM C 1383. The detailed description is as follows. The thickness (T) of the concrete plate is 0,2m, which is the value to be measured. First, the distance-setting step is performed: The thickness of the printed version (T) is 0.2m, which is printed by the employee's consumer cooperative of the Intellectual Property Bureau of the Ministry of Economic Affairs, and the formula (5) is substituted into the minimum distance (H). ; 2 XTX tan50.0 ° > 2 x 0.2 x tan 50.5 ° > 〇.485m Therefore, the distance from the strike source to the second receiver 22 later must be greater than the minimum distance (H). 15 This paper size applies to China National Standard (CNS) A4 (210 X 297 Public Love " 1231362

Printed by the Consumer Cooperative of the Intellectual Property Bureau of the Ministry of Economic Affairs. 5. Description of the invention (called the second step of tapping. Refer to Figures 9A, 9B, and 9C. Tap and decide the tap time origin (t0). The distance from the tapping source to the second receiver 22 (⑴55mm is greater than the required minimum distance. A tapper capable of sensing the origin of the tapping time is used, and a sensing element (press (Electrical material), this device is to combine the first receiver 21 and the tapping source 10, and can directly obtain the origin of the tapping time. Figure 9B shows the signal obtained from the tapping. The point (t0) is -40.0. Welding at this time is negative because the data acquisition system sets the signal to 0 when the signal reaches the excitation threshold, and the effective signal generated by the tap usually occurs before the excitation. , Will be set to the pre-excitation mode (pr ^ tdgger mode), so the time origin will appear at a negative value, the present invention only needs the time between t0 and tp, as long as the relative time difference is taken, it does not affect the invention Accuracy. Third, stress wave reading steps: Figures 9A, 9B, and 9C. After tapping, read that the longitudinal wave reflection arrival time (%) of the second receiver 22 is 133 2 焯, as shown in Figure 9c, and find the internal walking time of the longitudinal wave. (Λν = νΜ is ι33 · 2- (· 40.0) = 173.2 // s 〇 Fourth, the plate thickness frequency measurement steps: frequency measurement after the plate is the same as the previous ASTM C 1383 measurement, a second receiver 22 is set (Of course, the first receiver 21 can also be used instead.) As shown in Fig. 6a, the plate thickness frequency (heart) is obtained by performing a tap echo test. The measured displacement waveforms and spectrum diagrams are shown in Fig. 6B and As shown in Figure 6C, it shows the publishing thickness frequency (fT) = 9334Hz. 5 10 15 20 (Please read the notes on the back before filling this page) Order · ·; Line · 16 1231362 A7 B7 V. Description of the invention (〇 第V. Calculation steps: Calculate the tenth average longitudinal wave velocity (cP) of the flat thick sound m㈣ inside the concrete and the concrete version =. The internal longitudinal wave velocity (Cp) is equal to the actual walking distance divided by the internal 5 and this actual walking distance is used It can be obtained from the basic principle of A in Bishop's theorem, then formula (6), three

Cp (f) 2 + T2

At, substituting formula (3) into formula (6), we get formula (6)

Cp: ⑺ 10 15 Because the known thickness frequency (fT) and the internal walking time difference (AtJ), the ㈣ longitudinal wave velocity can be obtained from the formula （(Cpp then substitutes the obtained longitudinal wave velocity (Cp) into the formula (3). The thickness (τ) of the concrete plate can be obtained. When H = 0.55m 'fT = 9334Hz and Atp = 173.2 // s, the formula (7) can be substituted to obtain the internal longitudinal wave velocity (Cp) of 3947m / s, and then substituting this longitudinal wave velocity (Cp) into formula (3) to obtain the thickness of the concrete plate is 0.203m, and the measurement error is ι · 5%. Similarly, the second embodiment of the present invention is described as follows. The indirect method is to obtain the detection method of the tap time origin (t❹). This indirect method uses the wave propagation time method to invert the tap time origin. Therefore, in the above measurement step, the amount of surface R wave velocity needs to be increased. (This R-wave velocity measurement is a conventional technique.) For surface R-wave velocity measurement, please refer to Figures 10A, 10B, and 10C. Set a closer first receiver 21 next to a tapping source 10. And a farther 17 20 1231362 A7 V. Description of the invention (A) The second receiver 22 away, the first receiver 21 after hitting w The R-wave arrival times measured for the second receiver ^ 1 are (t0 and (t2), 12.0 // 8 and ... " S, the distance between the first and second receivers (L), L = 〇 i5m, and determine the surface R wave velocity with a conventional formula: 5 (CR) = L / h-ti) = 0.15 / (64-(-2.0)) = 0.15 / 66 = 2272 (m / s); With R; pico speed, τ performs the aforementioned five measurement steps. The first step is a fixed distance step, the configuration diagram is shown in Figure X-A, and the distance between the second receiver 22 and the striking source is H, 55m, the distance between the first receiver 21 and the tapping source 10 is A = 0.15m; the second step is the tapping step and the tapping time origin (tQ) is determined. After tapping, the _receiver 21 and the The waveform signals of the two receivers 22 are shown in the results of Figure 11B and Figure 11c, where the time when the R wave reaches the -receiver 21 is ti == _ 53 ·, and the origin of the tapping time should be pushed forward to R The time required for the wave to travel through distance A, that is, 10 15 ㈣bu (poor) = — 53 · 4 — = —119 Umbrella Ministry of Economic Affairs Intellectual Property Bureau employee consumer cooperative printing 20 The second step is the stress wave reading step, see Figures 11A, 11B and 11c, after tapping Read the longitudinal wave of the second receiver 22 through the background of the plate. The arrival time (tp) is 55 · 4 ^ as shown in Figure 11c, and the longitudinal travel time (AWt.) Of the longitudinal wave is 55 · 4-(_ 119 · 4) = 174 · 8%. The fourth step is the plate thickness frequency measurement step, and the plate thickness frequency fT is also 9334Ηζ, and then the fifth calculation step is performed, and the 18 and ____ 15 forest countries are obtained in the third and fourth steps. Standard (CNS) A4 size (210 X 297 mm 1231362 A7

V. Description of the invention () and fT = 9334 Hz are substituted into formula (7), then 4 ° 卩 longitudinal wave velocity (Cp) is 3891m / s, and then this longitudinal wave velocity (cd) is substituted into 々 々 PP; n into The thickness (T) of the concrete plate obtained by the formula (3) is 0.200 m, and the measurement error is 0.00%. As mentioned above, the plate thickness and thickness 5 obtained after two measurements by the method of the present invention are all 0.2015m, and the average error is only 0.75%, which is far lower than 2.5% of the conventional method, which greatly improves its accuracy. Investigate the reason ’As the interior of the concrete is not a homogeneous material (mixed with stones, sand, etc.), the P-wave velocity on the surface and inside is not the same. However, because this method of calculation uses the internal longitudinal wave velocity (Cp) of the actual internal reflection instead of the surface longitudinal wave velocity (cp) to estimate, the natural energy has higher accuracy and is very reasonable. The above is only a detailed description of the present invention through a preferred embodiment, and any simple modifications and changes made to the embodiment will not depart from the spirit and scope of the present invention. From the above detailed description, those skilled in the art can understand that the present invention can indeed achieve the stated purpose, and that it has complied with the provisions of the Patent Law, and filed an application for an invention patent. 10 15 (Please read the notes on the back before filling out this page) Order printed by the Consumers ’Cooperative of the Intellectual Property Bureau of the Ministry of Economic Affairs [Annex] 20 Annex 1: American Testing and Materials Association Standard Measurement Specification ASTM C 1383 Photocopy in duplicate 19 This paper size applies to China National Standard (CNS) A4 (210 X 297 mm)

Claims (1)

1231362 A8 B8 C8 D8 Patent application scope 10 15 Printed by the Consumer Property Cooperative of the Intellectual Property Bureau of the Ministry of Economic Affairs 20 kinds of methods to detect the internal longitudinal wave velocity and thickness of the concrete plate by stress waves, including the following steps: 1. The distance setting step: rough estimation Detect the plate thickness (T), prepare a first receiver and a second receiver, determine the appropriate minimum distance (Η) between the second receiver and the striking source, and make the striking source and the second The distance between the receivers must be greater than this minimum distance (Η), where the minimum distance (Η) must satisfy the following formula: ^ r ^ 27Txtan50.5 ° 2. Stroke step: Read the first receiver and The second receiver measures the time (ti) and (tp) and decides the tap time origin (t.). Among them, if a tapping device capable of sensing the origin of the tapping time is used, L is directly obtained as tQ; if the tapping time origin is obtained in an indirect way, the R wave velocity (CR) must be measured first, and then used indirectly. The wave transmission time method reversely strikes the origin of the time, then (") = the distance from the striking source to the first receiver (A) / the surface R wave velocity (CR); III. Stress wave reading steps: reading The longitudinal wave of the second receiver passes through the bottom reflection arrival time (tp) of the plate, and the time difference (Atp = tp-t0) is obtained; and the thickness measurement step of the plate thickness: a frequency measurement receiver is set up to perform a tap echo test Measure the plate thickness frequency (fT); Calculation steps: Use the following two formulas: Four or five paper sizes are applicable to China National Standard (CNS) A4 specifications (210X297 mm) (Please read the precautions on the back before filling this page) 1231362 The scope of patent application is Cp m In · and 2 10 T _ 0.96Cp, and the internal longitudinal wave velocity (Cp) inside the concrete and the thickness (T) of the concrete plate are calculated. As described in item i of the patent application, the method for detecting the internal longitudinal wave velocity and thickness of a concrete plate by a stress wave, wherein the plate thickness frequency (fT) is obtained by using a fast Fourier transform (FFT) technique to convert the second receiver After the measured digitized waveform is transferred to the spectrum domain to obtain the spectrum content, the high amplitude spikes in the spectrum diagram. The method for detecting the internal longitudinal wave velocity and thickness of a concrete plate by a stress wave as described in item 1 of the scope of the patent application, wherein the first receiver is provided on the striking source. (Please read the precautions on the back before filling this page) • Packing. Order Printed by the Consumer Cooperatives of the Intellectual Property Bureau of the Ministry of Economic Affairs This paper size applies to China National Standard (CNS) A4 (210X297 mm)