LY/T 3218-2020Test methods for floor vibration performance of timber structures (English PDF)

5.1 Excitation device

5.1.1 Vibration exciter

Vibration exciters include electric vibration exciters, electro-hydraulic vibration exciters, piezoelectric vibration exciters, etc., which are used to excite the vibration of the structure and should meet the following requirements Claim.

a) The excited modal test signal has a sufficient signal-to-noise ratio and does not produce a nonlinear response;

b) Applicable excitation mode and frequency components cover the frequency to be measured.

5.1.2 Pulse excitation device

The pulse excitation device can be an instrumented force hammer equipped with a built-in force sensor, or an impact device equipped with an independent force sensor. Pulse excitation equipment it is suitable to set the impact head with a weight of more than 10 kg and a rubber material.

5.1.3 Force sensor

The force sensor is calibrated according to the factory instructions before use, and the calibration process is described in GB/T 11349.2.The frequency response range of the force sensor is 0.5Hz~1kHz.

5.2 Acceleration sensor

The acceleration sensor is calibrated according to the factory instructions before use, and the calibration process is shown in JB/T 6822.Acceleration sensor frequency response range the range is 0.5Hz~1kHz, and the amplitude accuracy is ±1dB.

5.3 Data acquisition device

It is used to collect and store vibration signal data, analyze and record the time signal and extract the required information. The data acquisition device should be equipped to at least 2 analog input channels are needed to collect excitation force signal and wooden floor response signal at the same time. The sampling frequency should be more than 2 times the highest frequency to be tested Above, in order to capture the natural frequency characteristics of the floor to be tested, the output result of the signal analyzer should at least include the frequency response function and the coherence function.

The front end of the hardware analog signal acquisition of the data acquisition device shall have an analog anti-aliasing filter, and the cut-off frequency of the filter shall be greater than that of the wooden floor structure the highest analysis frequency, and the filter attenuation steepness outside the band is greater than 80dB/Oct; the acquisition instrument has an independent analog-to-digital converter (A/D) of more than 24 bits, the highest frequency is greater than 51.2 kHz, which meets the standard accuracy of JJG 834 dynamic analyzer class A.

5.4 Deflection test device

The accuracy of the deflection test device should be 0.3% of the expected deflection. Refer to JJF 1305 for the calibration process.

6.1 Modal test

6.1.1 Test requirements

During modal testing, the location of excitation point and response measurement should be selected appropriately to ensure that the natural frequency, modal damping ratio, modal shape, etc. can be obtained Modal parameters. Use a fixed point and a series of moving points for frequency response measurement, the number of frequency response measurements should be greater than or equal to the expected the number of desired modes.

Modal test steps should include selection of excitation position, selection of response measurement position, sensor installation, excitation test, and verification of measurement results.

And modal analysis. Excitation test can use vibration exciter or pulse excitation method.

6.1.2 Excitation location selection

The excitation position should avoid the nodes of the mode shape of interest, and should be selected at 1/6 of the floor width and near the center of the floor span.

6.1.3 Response to measurement location selection

The number of response measurement points should be large enough to ensure that the mode shape of interest can be obtained. If the floor is a joist structure, the grid method should be used to confirm Determine the measuring point, divide the floor slab into 3 equal parts in the vertical direction of the joists, and cross the joists to form a grid. If the floor is a flat structure such as orthogonal glulam, the measuring points should be evenly arranged and located at the connection between the center of each plate and the adjacent plates.

6.1.4 Sensor installation

If the excitation method is impulse excitation such as force hammer, the force sensor should be built into the excitation device.

The acceleration sensor should be tightly bonded to the upper part of the floor. If the upper part of the floor slab is covered with carpet, a special type that can penetrate the carpet to reach the floor slab should be used.

With the mounting base, the acceleration sensor can be glued to the base. If the floor is paved with a floor or a concrete surface, the acceleration sensor can be directly glued Connect to the upper surface of the floor or concrete surface.

6.1.5 Excitation test of the exciter

6.1.5.1 Vibration exciter installation

The exciter should be placed on a solid ground to excite the floor from below. If this is not possible, use a spring to suspend the exciter on the floor to be tested Part to ensure that the natural frequency of the suspension exciter system is less than one-tenth of the natural frequency of the floor to be tested.

The exciter applies excitation to the floor through the transmission rod, as shown in Figure 1.The transmission rod should have sufficient rigidity to transmit the predetermined excitation force.

Figure 1 Schematic diagram of the vibration exciter installation

6.1.5.2 Excitation mode

The excitation mode adopts random excitation.

6.1.5.3 Measurement settings

a) Add a Hanning window to the time domain signal;

b) Monitor the coherence function and determine the minimum number of measurements of the floor frequency response function, which should be no less than 5 times, and the sampling time should be more than 5 minutes;

c) Set the sampling frequency. The sampling frequency should be more than 2 times the maximum value of the natural frequency concerned, and the control frequency resolution should not be greater than 1% of the first-order natural frequency of the floor, as shown in equation (1).

6.1.6 Pulse excitation test

6.1.6.1 Measurement settings

a) Monitor the coherence function and determine the minimum number of measurements of the floor frequency response function, which should be no less than 5;

b) Set the sampling frequency. The sampling frequency should be more than 2 times the maximum value of the natural frequency concerned, and the control frequency resolution should not be greater than 1% of the first-order natural frequency of the floor;

c) Add a rectangular window to the excitation signal, and an exponential window to the transient response signal; if the acceleration response signal at the end of the time-domain signal record is attenuated to 1% of the initial value, there is no need to add an exponential window;

d) The exponential window will increase the damping of the measurement response signal and should be corrected according to formula (2).

6.1.6.2 The influence of the operator on the floor slab test There should be no operators on the upper part of the floor to be tested during the test. If there is an operator on the upper part of the floor, it should be noted in the test report. Operator treatment the influence of floor slab frequency can be estimated with floor dynamics model, see Appendix A.

6.1.7 Verification of measurement results

The coherence function is used for verification. The value of the coherence function should be between 0 and 1, generally greater than 0.8.When the coherence function is low, you should check Explain the reasons and take measures to improve.

After the floor test is completed, the excitation points and response points are exchanged to check the reciprocity, and then the floor slab is modal tested. Measure the frequency response function the results are compared with the previous test results. If there is a difference, it indicates that the sensor is installed improperly or there is a non-linear signal.

6.1.8 Modal analysis

The natural frequency, modal damping ratio and mode shape of the floor slab are extracted from the frequency response function. If there is an operator on the upper part of the floor to be tested, from the frequency response letter the natural frequency of the floor slab extracted from the number refers to the estimation result in Appendix A.

6.2 Static load deflection test

6.2.1 Test requirements

The static load deflection can be measured from the lower or upper part of the floor, depending on the construction details of the floor. For the test floor slab is equipped with soft the surface course or decorative surface course shall be tested from the lower part of the floor, and the measuring surface shall be at the bottom of the floor joist or slab.

6.2.2 Installation and fixing of deflection measuring device

6.2.2.1 Installation of the lower part of the floor

The test benchmark should be the ground or floor below the floor to be tested, as shown in Figure 2.The deflection meter is fixed on the supporting rod, and the measuring rod of the deflection meter is connected to the the bottom of the floor joist is in close contact, and the deflection meter is reset to zero.

Figure 2 Schematic diagram of the lower part of static load deflection measurement

6.2.2.2 Installation of upper floor

The test benchmark should select the outer boundary of the floor, and there is a wall support below the boundary. Both ends of the test reference beam are supported on the outer edge of the floor the part should have sufficient rigidity and no additional deformation. The deflection gauge is installed on the reference beam and reset to zero. Test reference beam erection and deflection measuring device the schematic diagram of the installation is shown in Figure 3.

6.2.3 Applying the load

Use a testing machine, a constant mass heavy object or a person to apply a concentrated load, and the mass of the heavy object or person should be measured immediately after the deflection measurement is completed.

6.2.4 Data logging

If the deflection of the center of the floor slab is obtained, a load should be applied to the center of the floor slab, and the deflection after the load is applied should be recorded. If a constant mass weight is used or personnel, should ensure that the floor deformation is in the elastic range, and determine the deflection of the specified load according to the load-deflection linear relationship.

If the distribution of deflection of the floor slab under concentrated load is obtained, the load should be applied in the center of the floor slab. If the floor is a joist structure, measure the span of each joist If the floor is a heavy-duty slab structure, measure the deflection at the center of each slab. It can also be used in the middle of each joist or the center of each board.

The load is applied one time and the deflection of the center of the floor slab is measured.