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Ding, Y., Zhang, Y., Wang, Z., Gao, Z., Zhang, T., and Huang, X. (2020). "Vibration test and comfort analysis of environmental and impact excitation for wooden floor structure," BioRes. 15(4), 8212-8234.

Abstract

To meet consumer requirements for comfort in wooden structure construction, test mode methods (the environmental excitation method and impact excitation method) have been used to test six measuring points of the flooring in a two-story residential light-wood structure. The following tests were performed: the fundamental frequency test of floor structure under environmental excitation mode; the ball excitation dynamic vibration test of single and rhythmic running of a basketball and tennis ball under impact excitation mode; and the pedestrian dynamic vibration test of jump, single-step, steady walking, and rhythmic movement. The comfort analysis was validated based on the test results of peak value and effective value of fundamental frequency, acceleration, and speed. ANSYS was used to verify the calculation mode of the floor structure. Research showed that the fundamental frequencies of the building structure obtained through the calculation mode and the test mode were consistent, and both were higher than 4.5 Hz. The maximum measured acceleration peak value under the impact excitation mode was 407.2 mm/s2. The maximum speed peak value was 5.606 mm/s. The maximum acceleration effective value (RMS) was less than 450 mm/s2. The floor structure results met the building comfort requirements. The research has value in engineering applications, as it advances understanding concerning the vibration characteristics and comfort optimization of light-wood frame construction.


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Vibration Test and Comfort Analysis of Environmental and Impact Excitation for Wooden Floor Structure

Yewei Ding,a Yifan Zhang,a Zheng Wang,a,* Zizhen Gao,a Tongyue Zhang,a and Xiuling Huang b

To meet consumer requirements for comfort in wooden structure construction, test mode methods (the environmental excitation method and impact excitation method) have been used to test six measuring points of the flooring in a two-story residential light-wood structure. The following tests were performed: the fundamental frequency test of floor structure under environmental excitation mode; the ball excitation dynamic vibration test of single and rhythmic running of a basketball and tennis ball under impact excitation mode; and the pedestrian dynamic vibration test of jump, single-step, steady walking, and rhythmic movement. The comfort analysis was validated based on the test results of peak value and effective value of fundamental frequency, acceleration, and speed. ANSYS was used to verify the calculation mode of the floor structure. Research showed that the fundamental frequencies of the building structure obtained through the calculation mode and the test mode were consistent, and both were higher than 4.5 Hz. The maximum measured acceleration peak value under the impact excitation mode was 407.2 mm/s2. The maximum speed peak value was 5.606 mm/s. The maximum acceleration effective value (RMS) was less than 450 mm/s2. The floor structure results met the building comfort requirements. The research has value in engineering applications, as it advances understanding concerning the vibration characteristics and comfort optimization of light-wood frame construction.

Keywords: Wooden floor structure; Environmental excitation; Impact excitation; Vibration test; Natural frequency; Comfort analysis

Contact information: a: College of Materials Science Engineering, Nanjing Forestry University, Nanjing, China 210037; b: College of Mechanical and Electronic Engineering, Nanjing Forestry University, Nanjing, China 210037; *Corresponding author: wangzheng63258@163.com

INTRODUCTION

With improved living standards, people have increased demands for building comfort. The floor, roof, and shear wall are the three main structural systems of light-wood frame construction, and all influence comfort. As the most common structural system, the wooden floor is also a system that often has physical contact with the occupants (Yang et al. 2019). The vibration frequency of the wooden floor structure is generally above 8 Hz. Usually wooden buildings have a small number of floors and a small area, and there are fewer events causing safety problems due to its low natural frequency. However, because of the defects or deficiencies in the floor structural performance, the dynamic movement of people or objects in the living environment may cause discomfort to the occupants. Movements, such as walking, running, jumping, falling, etc., easily cause structural vibration in a wooden floor, which will seriously affect work efficiency and living quality in severe cases (Zhang and Xie 2011). The frequency range that has obvious influence on the human body is generally between 0 and 50 Hz. The wooden floor can be regarded as a continuum, and its vibration frequency is infinite. Due to its inherent structural dynamic characteristics, it is necessary to perform the building comfort analysis using the on-site dynamic vibration performance testing according to the structural dynamic principle (Wang et al. 2019a).

Researchers worldwide have made abundant research achievements on floor vibration. Jarnerö et al. (2015) tested natural frequency and damping ratio of prefabricated wooden floor units under different construction stages and different boundary constraints in the laboratory. The results show that under different states, the tested damping ratios are notably different. Rijal et al. (2016) conducted a modal test on a wooden floor with 6- and 8-m-span beams, and analyzed its natural frequency, damping ratio, and vibration mode. Their results show a good correlation between the test values and predicted values.

In China, the research on floor vibration is mainly based on concrete structures and steel structures. The specification JGJ 3-2010 (2010), “Technical specification for high-rise building concrete structures,” proposed that the vertical vibration frequency of floor structures should not be less than 3 Hz, and stipulated the recommended limits for values of vertical vibration acceleration, floor structure acceleration caused by human walking, and vibration acceleration caused by rhythmic running. The “Code for design of concrete structures” or GB 50010-2010 (2015) stipulates that the vertical natural vibration frequency of concrete floor structures, such as residences and apartments, shall not be lower than 5 Hz. The “Code for design and construction of composite floor slab” or CECS 273-2010 (2010) specifies the limit of the peak value of vibration acceleration.

Although research in China concerning modern wood frame construction started late, it has developed rapidly in recent years, and preliminary research results have been obtained regarding wooden floor vibration. Zhou (2006) summarized the research progress on the relevancy of the design method on wooden floor vibration, and noted the problems with current design development and point out the direction of further research. Lu et al. (2010) analyzed the vibration acceleration response of floor structures with pedestrian load, and proposed an analysis method using the frequency-weighted root mean square value of acceleration as the evaluation index. Lu et al. also analyzed the variation between the law of the vertical vibration intensity and the fundamental frequency. On the basis of domestic and foreign research, Huang et al. (2011) proposed a comfort design standard considering the rhythmic running and derived a formula of vibration acceleration according to the dynamic principle. They also elaborated in detail the load value determination and the analysis of the working conditions of the floor structure vibration calculation. These results can provide reference for the vibration comfort design of the floor under the action of rhythmic running. Li (2012) studied the three-story large-span cantilevered floor of Dalian Citizen Fitness Center for comfort analysis and vibration control under the action of human activities. The dynamic response of the large-span cantilevered floor under the crowd load was calculated and evaluated by using SAP2000 through a different model: a single-step load model, a single person continuous walking, a rhythmic running load model, and a random load model. The floor structure vibration was controlled by the design of reasonably tuned mass damper (TMD) parameters.

In view of the entire introduction, the current paper conducted a fundamental frequency test on a floor structure under environmental excitation mode; the ball excitation dynamic vibration test of single and rhythmic running of basketball and tennis under impact excitation mode; and the pedestrian dynamic vibration test of a single-step, jumping, steady walking, and rhythmic running based on the floor structure of a two-story assembled light-wood structure residence (Wang et al. 2019b). The comfort analysis was validated based on the test results of peak value and effective value of fundamental frequency, acceleration, and speed. This research is valuable to meet people’s objective requirements for building comfort, and to provide reference for the design optimization of wooden floor structures.

EXPERIMENTAL

Materials

Test object

A two-story light-wood frame construction (a structure for tool storage) was used for testing. Its external dimensions were 6100 mm long × 2576 mm wide × 3396 mm high, and its internal dimensions were 6042 mm long × 2460 mm wide × 3230 mm high. The external dimensions of the floor structure as the test object are shown in Table 1 and Fig. 1. All materials of the wooden floor structure were fixed by nailing.

Table 1. Wooden Floor Structure Composition

Fig. 1. Schematic diagram of wooden floor

Instruments and accessories

(1) The vibration and dynamic signal acquire analysis system (CRAS) and dynamic signal acquisition and analysis system of Nanjing Anzheng Software Engineering Co., Ltd. (Nanjing, China), were used. They primarily included a signal acquisition box, a signal conditioning box, a working station installed with AdCRAS analysis software (Version 8.0, Nanjing, China), SsCRAS analysis software (Version 8.0, Nanjing, China), and Origin Pro software (Version 9.0, Northampton, MA, USA). The system had acquisition and analysis functions, including data acquisition, signal analysis, system analysis, noise analysis, and modal analysis, which were realized by dedicated software.

(2) Four 941B vibrators of the Institute of Engineering Mechanics of the China Earthquake Administration (Wuhan, China) were used. Each vibrator’s size was 63 mm × 63 mm × 80 mm, with a weight of 1 kg. The acceleration gear (maximum measuring range 20000 mm/s2) and second speed gear (maximum measuring range was 125 mm/s, displacement 20 mm) were adopted.

(3) Other accessories, such as steel tape, double-sided tape, etc. were also used.

Calculation mode

Mechanical performance test of base material of floor cover

Seven samples of OSB board, maple floor and SPF each with an average moisture content of 12%, 9% and 12% were randomly selected to test the elastic modulus, shear modulus, and Poisson’s ratio (Wang et al. 2018). Table 2 shows the mechanical properties of the tested materials.

Table 2. Material Mechanical Properties

Building a floor model

ANSYS software was used to model the fabricated light wood building floor. Based on simulation data required for the test, beam188 and shell181 units were used to input the relevant parameters of floor structure to the model to obtain the vibration shape of the floor and its corresponding frequency. Figure 2 shows the finite element model of the floor.

Fig. 2. Model of floor structure

Methods

Environmental excitation test method – Test principle and test block diagram

The block diagram of the spectrum test of wooden floor is shown in Fig. 3 The vibrator placed on the wooden floor received the environmental vibration signal and converted it into an electrical signal output. After the signal conditioner amplified and filtered the electrical signal, the Analog-to-Digita (AD) analog signal was converted into a digital signal by the acquisition box. After analysis and processing by software, the natural frequency value spectrum of the wooden floor was obtained (ISO/AWI 2631-1 1997; ISO 2631-2 2003).

Fig. 3. Test block diagram of floor spectrum

Main Test Steps

(1) Test sites were selected. To obtain better fundamental frequency measured in the measuring point, six measuring points were used, and each measuring point was tested twice, as shown in Fig. 4.

Fig. 4. Distribution of test points

(2) The instrument was connected and the wiring checked. The vibrators were placed and fixed at six test points, and the second speed gear and acceleration gear were used.

(3) Parameters were set, and the oscillations began. The unit of the speedometer was mm/s, the environmental excitation mode was used in a voltage range between 0 and 1250 mV and the analysis frequency of 50 Hz, and the AdCras software was also used to oscillate, check, and adjust the amplification factor.

(4) Data was collected and the test was repeated twice.

Impact Excitation Test Method

Test principle and test block diagram

The test spectrum block diagram was the same as shown in Fig. 3. As shown, the vibrator placed on the wooden floor received an impact vibration signal and converted it into an electrical signal output. After the signal conditioner amplified and filtered the electrical signal, the acquisition box converted the analog signal AD into a digital signal. The natural frequency spectrum of the structure was obtained by software analysis.

Ball excitation test method

The ball excitation comprised of both a single-time excitation on the floor and regular knocks on the floor, the latter of which fell freely and regularly at a frequency of 2 Hz and a height of 1 m to test the acceleration peak, effective acceleration, speed peak, and effective speed.

Pedestrian excitation test method

(1) Jump excitation test

The main steps of the jump excitation test of the wooden floor (Lin 2015) were as follows: connect the vibration and dynamic signal acquisition and analysis system instruments, and check the wiring; respectively place the 941B vibration absorbers at each measuring point on the wooden floor; set SsCras software parameters (the units of accelerometer and speedometer were mm/s2 and mm/s, respectively, the analysis frequency was 50 Hz); the tester with a weight of 60 kg was in the range of 100 ± 30 mm at the test point, and oscillating was performed; the experimenter collected the frequency spectrum of the jump excitation test (the jumping height was 150 mm). The test was repeated twice.

Fig. 5. Schematic diagram of single-step excitation

(2) Single-step excitation test

Figure 5 shows the single-step excitation curve (Lin 2015), where the nominal force was the ratio of vertical force to human weight. The force at point B was 1.20 to 1.25 times the human weight, while the force at point D was approximately 1.15 times the human weight.

(3) Steady walk excitation test

The experimenter with a weight of 60 kg walked steadily at a frequency of 2 Hz on the wooden floor (Lou 2011).

(4) Rhythmic running excitation test

The experimenter with a weight of 60 kg ran steadily at a frequency of 4 Hz on the wooden floor (Xu et al. 2008).

RESULTS AND DISCUSSION

Finite Element Simulation Results

Through ANSYS modal analysis, the fundamental frequency of the overall building slab model was 16.413 Hz. Figure 6 shows a bending mode and its corresponding frequency in the length and width directions of the floor.

Fig. 6. The first-order vibration mode of floor model simulation

Environmental Excitation Test Results

Under environmental excitation mode, the fundamental frequency test results of measuring points 1 through 6 of the wooden floor were obtained, as shown in Table 3. The mean value, standard deviation, and coefficient of variation were 17.50 Hz, 0.075, and 0.04%, respectively.

Table 3. Environmental Excitation Test Results for Points 1 Through 6

Impact Excitation Test Results

Ball excitation test results

(1) Basketball single excitation test

The test results of the acceleration, speed, and fundamental frequency values of the single excitation test of a basketball at 1 through 6 are shown in Table 4. Figure 7 is the spectrum diagram of point 2.

Table 4. Acceleration, Speed, and Natural Frequency Values of a Single Excitation Test of a Basketball at Points 1 through 6

Fig. 7. Spectrum diagram of the single excitation test of a basketball at point 2

(2) Tennis ball single excitation test results

The test results of the acceleration, speed, and frequency values of a single excitation test of a tennis ball at points 1 through 6 are shown in Table 5.

Table 5. Acceleration, Speed, and Natural Frequency Values of a Single Excitation Test of a Tennis Ball at Points 1 Through 6

(3) Basketball rhythmic excitation test results

The test results of the acceleration, speed, and frequency values of a basketball’s rhythmic excitation at points 1 through 6 are shown in Table 6.

Table 6. Acceleration, Speed, and Natural Frequency Values of Rhythmic Excitation Tests of a Basketball at Points 1 through 6

(4) Tennis ball rhythmic excitation test results

The test results of the acceleration, speed, and frequency values of a tennis ball’s rhythmic excitation test at points 1 through 6 are shown in Table 7.

Table 7. Acceleration, Speed, and Natural Frequency Values of Rhythmic Excitation Tests of a Tennis Ball at Points 1 Through 6

Pedestrian Excitation Test Results

(1) Jump excitation test results

The test results of the acceleration, speed, and frequency values of the jump excitation test at points 1 through 6 are shown in Table 8. Figure 8 is the spectrum diagram of the jump excitation test at point 4.

Table 8. Acceleration, Speed, and Natural Frequency Values of Jump Excitation Tests of a Tennis Ball at Points 1 Through 6

Fig. 8. Spectrum diagram of the jump excitation test at point 4

(2) Single-step excitation test results

The test results of the acceleration, speed, and frequency values of the single-step excitation test at points 1 through 6 are shown in Table 9.

Table 9. Acceleration, Speed, and Natural Frequency Values of Single-step Excitation Tests of a Tennis Ball at Points 1 Through 6

(3) Steady walk excitation test results

The test results of the acceleration, speed, and frequency values of steady walking excitation tests at points 1 through 6 are shown in Table 10. Figure 9 is the spectrum diagram of steady walking excitation tests at point 5.

Table 10. Acceleration, Speed, and Natural Frequency Values of Steady Walk Excitation Tests of a Tennis Ball at Points 1 Through 6