- Email: [email protected]
Rapid evaluation of safety-state in hidden-frame supported glass curtain walls using remote vibration measurement
Author’s Accepted Manuscript Rapid Evaluation of Hidden Frame Supported Glass Curtain Wall Safety State Based on Remote Vibration Measurement Zhide Huang, Mowen Xie, Jinhui Zhao, Yan Du, Hong-ke Song www.elsevier.com/locate/jobe
PII: DOI: Reference:
S2352-7102(18)30215-8 https://doi.org/10.1016/j.jobe.2018.04.030 JOBE475
To appear in: Journal of Building Engineering Received date: 23 February 2018 Revised date: 28 April 2018 Accepted date: 28 April 2018 Cite this article as: Zhide Huang, Mowen Xie, Jinhui Zhao, Yan Du and Hong-ke Song, Rapid Evaluation of Hidden Frame Supported Glass Curtain Wall Safety State Based on Remote Vibration Measurement, Journal of Building Engineering, https://doi.org/10.1016/j.jobe.2018.04.030 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Rapid Evaluation of Hidden Frame Supported Glass Curtain Wall Safety State Based on Remote Vibration Measurement Zhide Huang1,2, Mowen Xie1,*, Jinhui Zhao3, Yan Du1, Hong-ke Song1 1
School of Civil and Resource Engineering, University of Science and Technology Beijing, Beijing, 100083, China 2 School of Civil Engineering, Inner Mongolia University of science and technology, Baotou, Inner Mongolia, 014010, China 3 Shenzhen Taike test CO,LTD, Shenzhen, Guangdong, 518053, China Corresponding author. [email protected]
Abstract The vibration performance of simulation hidden frame supported glass curtain wall (HFSGCW) was tested using Laser Doppler Vibrometer (LDV) in this paper. The effect of silicon structural sealant on the first order inherent frequency of HFSGCW and the spectral characteristics got by LDV on different points were studied. Meanwhile, the test results of LDV were verified using traditional sensor (DASP modal analysis system) in order to evaluate the feasibility of LDV used for safety state evaluation of HFSGCW. The results show that the first order inherent frequency obtained by LDV matches well with DASP modal analysis results. The first order inherent frequency decreases with the increase of sealant failure, and increases significantly when the structural silicon sealant was completely destroyed. The safety state of HFSGCW was divided into three levels. Meanwhile, the safety state rapid evaluation model and key detection technologies of HFSGCW based on LDV was proposed.
Key words: Laser Doppler Vibrometer (LDV), Hidden frame supported glass curtain
wall (HFSGCW), Modal analysis, Safety state, Evaluation model
Main symbols HFSGCW-Hidden Frame Supported Glass Curtain Wall DASP-Data Acquisition & Signal Processing, a modal measure and analysis system produced by China Orient Institute of Noise & Vibration LDV-Laser Doppler Vibrameter SISO-Single Input Single Output
f DASP ,n -nth order modal frequency measured by DASP f LDV ,n -nth order modal frequency measured by LDV f n -nth order modal frequency
n -nth order modal damping ratio 1 Introdution Hidden frame supported glass curtain wall (HFSGCW) is light in mass, transparent, and relatively energy efficient, which is a kind of new technology product. The aluminum alloy outline border is removed and the glass panels are cohered on the metal framework through structural silicon sealant. The quality guarantee period of structural silicon sealant is usually 10 years [1,2], which means that the existing HFSGCWs built on 10 years ago are under challenges such as the aging of structural silicon sealant, the decrease of bonding force, the possibility of shedding and so on[3,4]. Meanwhile, the project quality field detection contents of existing curtain wall mainly focus on the appearance quality such as geometry size, coating film thickness, corrosion situation. The detection criterion can reflect the physical condition of HFSGCWs, but cannot reflect the safety state of HFSGCWs. Therefore, the prevention of glass falling off and decrease of casualty loss are urgently needed to be solved for HFSGCWs. The previous researches are mainly focused on the monolithic reliability
assessment of HFSGCW [5-9], and there is less result about the damage identification of curtain wall glass panel. Bendon and Amadio [10-13] studied the shear, lateral-torsional buckling of curtain wall glass panels restrained by different boundary condition. They gives three different restraint boundary conditions of glass curtain wall: 1) linear adhesive joints along the top and bottom edges only 2) supporting metal frames with interposed linear adhesive joints and 3) mechanical point-fixing connectors. Chen et al. [14] conducted the impulse response experiment on glass curtain wall and the experimental data was calculated using Gaussian and Lorentzian function. The relation between the propotion of FFT main peak frenquency to signal total power and the damage length of structural sealant was set up. However, this method was based on the mode of power spectral density and sealant failure length, and the application range of the model also needed to be determined. Fang et al. [15] analyzed the modal of curtain wall under different constraint using ANSYS finit element software. They proposed that the damage condition of structural sealant can be recognized through modal curvature change features. However, this method is based on the structural modal analysis and belongs to the follow-up work after the confirmation of safety state. The safety state of exposed frame glass curtain wall was simulated by Liu et al. [16, 17] through adjusting the bolt tightness degree of alloy shell frame. They also verified the feasibity of using inherent frequency to evaluate the tightness degree of curtain wall shell frame, and they built simple evaluation model based on two boundary conditions including four sides clamp support and simply support. They considered that the inherent frequency lower limit of curtain wall at work is the inherent frequency under four sides simply support. However, the conclusions do not contain the free boundary condition caused by local adhesive failure damage. Above all, evaluating the safety state using dynamic characteristics
has been done mainly based on numerical simulation and tradition modal testing method, and the researches are mainly targeted at exposed frame glass curtain wall. The related research about HFSGCW is rarely. Meanwhile, the tradition contacted sensor used for modal testing and analysis consume a mass of labor and time, so the practicability is heavily discounted in practical detection. The inherent frequency of HFSGCW under different working condition was tested through LDV and traditional sensor (DSAP) respectively in this paper. The research results will provide reference for safety state evaluating of existing HFSGCW. Meanwhile, the safety state evaluation model of HFSGCW was built and the safety state level was divided. 2 Vibration theory As an intrinsic characteristic, the structure vibration performance is closely related to boundary condition and physical property. The constraint of curtain wall shell frame to glass panel is reducing with the aging of structural sealant and the increment of service life. This means that the dynamic parameters change inevitably with the transformation of vibration theory boundary conditions, and this is the theoretical basis of curtain wall safety state evaluation. Curtain wall glass is typical thin-slab structure, and the lateral oscillation differential equation is [18]:
4w 4w 4w 4 2 w 0 x 4 x 2 y 2 y 4
（1）
Where
4
m 2 D
（2）
where is the inherent circular frequency of glass panel, rad/s; m is the mass per unit area of glass panel, kg/m2; D is the flexural rigidity of glass panel, N·m; a, b is the plan size of glass panel; the computational formula of flexural rigidity is:
D
Eh3 (1 2 ) 12
（3）
Where E is glass panel elasticity modulus; h is the glass panel thickness; is the glass panel Poisson ratio. The inherent circular frequency deduced from oscillatory differential equation is as follows. When the four sides of glass panel are clamp supported:
12
504 D 4 ( a 4 b 4 a 2b 2 ) 4 4 7 a ·b ·m
（4）
When the four sides of glass panel are simply supported:
1 2 (
1 1 D ) a 2 b2 m
（5）
The boundary condition of HFSGCW at work is between four sides clamp support and simply support, and the first order inherent frequency (f1, Hz)of the two boundary conditions respectively is as follows. When the four sides of glass panel are clamp supported:
f1
1 1 2 2
504 D 4 ( a 4 b 4 a 2b 2 ) 4 4 7 a ·b ·m
（6）
When the four sides of glass panel are simply supported:
f1
1 1 1 D ( ) 2 2 a 2 b2 m
（7）
3 Experimental programs 3.1 Instruments The vibration performance of HFSGCW is tested simultaneously using LDV (PDV-100, produced by Polytec Company, Germany) and DASP modal analysis system (produced by China Orient Institute of Noise&Vibration).
The working principle of LDV is Doppler Effect. When the vibrating object keeps way from the LDV, the wave length of reflected light elongates, and when the vibrating object is close to the LDV, the wave length of reflected light shortens. The LDV transmits HeNe laser beam to the object surface, and collect reflection light simultaneously. The vibration velocity of object is obtained by means of demodulating frequency shift signal based on Doppler Effect. The object vibration frequency domain curve is got through FFT and then the peak value is the object inherent frequency. Compared to traditional vibration sensor, the remote and non-contact properties of LDV give it the unique advantages in practical application, and the measurement accuracy far exceeds traditional contact sensor. Meanwhile, the LDV is not subject to environments. The LDV is show in Fig.1, and the working principle is shown in Fig.2. Table 1 shows the main technical parameters of LDV. As a traditional sensor, the result of DASP modal analysis system was used to verify the accurate of LDV. Fig.3 shows the set-up of DASP modal analysis system, and Table 2 shows the basic technical parameters of it.
Fig.1
LDV
Object Incident ray Reflected ray (a) Initial position
(b) The object come near, the wave length of the reflected ray shortens
(c) The object is away, the wave length of the reflected ray elongates
Fig.2 Measurement principle of LDV
Table 1 Technical parameters of LDV Frequency range Speed
Ranging scope 100 m
0.5Hz-22kHz
Curtain wall glass
Acceleration sensor
Exciting hammer
500 mm/s
Vibration signal
Signal collecting device
Resolution ratio 0.02 µm/(s·Hz0.5)
PC& DASP software package
Exciting signal
Fig.3 Set-up diagram of DASP modal analysis system
Type INV9822
Table 2 Technical parameters of the traditional sensor Sensitivity Frequency Range Resolution ratio 100 mv/g 0.5-8 kHz 50 g 0.002 m/s2
3.2 Raw materials The common tempered glass and single silicone structural sealant (MF899) [19] were used, and the parameters are shown in Table 3 and Table 4 respectively.
Side length, a/mm 600
State Pasty fluid
Table 3 Basic parameters of glass specimen Side length, Thickness Elasticity Density/(kg·m-2) b/mm /mm modulus/GPa 600 5 12.5 70
Color Black
Possion ratio, ν 0.24
Table 4 Properties of structural sealant Extrusion/s Shore hardness Tensile strength/MPa 1.8 43 2.1
3.3 Experimental design In order to simulate the frame support structure system of HFSGCW, the joist steel was fixed on the wall through anchor bolts, as shown in Fig.4 (a). The inner size of joist steel frame is 55cm×55cm, and the outside size is 69cm×69cm, as shown in Fig.4 (b). The curtain wall glass was pasted to joist steel frame using silicon structural sealant, as shown in Fig.4 (c) and Fig.4 (d). The width of the structural sealant is 2.5 cm and the thickness is 0.5 cm. The experimental photograph is shown in Fig.5 (a) and the corresponding measure point division is shown in Fig.5 (b). The glass was divided into thirty-six table cells and forty-nine measure points, and the reflector plate was pasted on the measure point. The DASP sensor was pasted on the ninth measure point using 502 glue [20].The standard working condition was in full adhesion, and the sealant failure was accomplished through cutting. The working condition in this paper was divided into six different situations on the basis of sealant failure, as shown in Fig.6. 70mm
60cm
69cm
Glue side
4.5mm
Anchor bolts 100mm
Steel frame 55cm
Sealant 69cm
60cm
Glass panel
55cm
7cm 7cm
Anchor side
(a)
(b)
(c)
(d)
Fig.4 Experimental apparatus. (a) Section dimension of steel frame; (b) Anchor side of steel frame; (c) Glue side of steel frame; (d) Experiment apparatus: steel frame ,sealant and glass panel
(a) Experimental photogragh (b) Table cell and measure point Fig.5 Glass curtain wall experimental photograph and measure point
27.5cm
Condition 1
Condition 2
Condition 3
40cm
Condition 4 Condition 5 Condition 6 Fig.6 Sealant failure illustration of different working conditions
3.4 Testing process The testing process was shown in Fig.7. Fig.7 shows that the modal analysis using DASP was conducted firstly, and then the dynamic test was done using LDV.
The DASP modal analysis system was based on SISO, and the ninth measure point was selected as the reference point. The variable time theory was used to sample. Three samples were conducted on every point. The sampling frequency is 51.2 kHz, and the variable-time multiple and the sensor frequency is 32 and 1600 Hz respectively. The analytical frequency is 800 Hz. The time-domain signal was translated into rumble spectrum signal through FFT. The sampling point was set as 8192. After that, frequency-response function calculation was done, and the average value was selected to be modal order. The fitting was done on the basis of complex mode and single degree of freedom in order to get the modal parameters and modal shape. The reflector plate was used to increase reflected signal in LDV test. The artificial excitation was chosen to trigger object. The sampling frequency is 1200 Hz, the bandwidth is 500 Hz, and the sample time is 6.4 s. The forty-nine points were all tested under every working condition, and the average first order frequency of all points was selected as the final first order inherent frequency. Condition 1
Modal test （DASPSISO）
LDV test
Results analysis
Cutting adhesive Modal test （DASPSISO）
Condition 3
……
Cutting adhesive LDV test
Clean the lab
Cutting adhesive
LDV test
Condition 6
Finish the test
Modal test （DASPSISO）
Modal test （DASPSISO）
LDV test
Cutting adhesive Condition 2
Fig.7 Testing process
4 Result and analysis 4.1 Comparative analysis of test results obtained by LDV and DASP Table 5 shows the test results of first order inherent frequency of six different working conditions. The first order inherent frequency obtained by LDV is in accordance with the results tested by DASP, which illustrate that the accurate measurement of dynamic parameter can be realized by LDV. Table 6 shows the discreteness of the LDV first order inherent frequency. The standard deviation of the first to fifth working condition is ±0.5 Hz, and the standard deviation of the sixth working condition is 1.67 Hz, which also shows that the LDV can realize the accurate measurement of HFSGCW dynamic parameter.
Table 5 Test results of first order frequencies of different working condition (Hz) f LDV f DASP f DASP f LDV Working condition 1 94.26 94.24 -0.02 2 90.33 90.61 0.28 3 88.35 89.13 0.78 4 80.38 79.43 -0.95 5 78.28 78.07 -0.21 6 49.71 49.95 0.24
Table 6 Discreteness of the test results (Hz) Working condition 1 2 3 4 5 6
Maximum
Minimum
Difference
94.84 91.56 89.69 80.16 78.59 53.59
93.16 89.06 87.34 78.44 76.25 46.72
1.68 2.5 2.35 1.72 2.34 6.87
Standard deviation 0.33 0.51 0.39 0.43 0.41 1.67
Fig.8 The first order vibration modal shape of HFSGCW
The vibration modal shape obtained by DASP was shown in Fig.8, in which the legend value is normalized by the maximum displacement. With the change of working condition, the modal shape has moving toward the sealant failure direction. However, because that structural sealant has not been fully broken, the cutting damage can only weaken boundary constraint, but cannot eliminate it. Therefore, the deviation of modal shape is not obvious between working condition 2 and 3. Similarly, this phenomenon occurs between working condition 4 and 5. 4.2 Sealant failure analysis As shown in Table 5, the first order inherent frequency of HFSGCW decrease with the increase of sealant failure, indicating that the safety state of HFSGCW can be determined by first order inherent frequency. Fig.9 shows that the sealant failure increment is the same from working condition 3 to 4 and from working condition 4 to 5, but the first order frequency range for the former is larger than that for the later. This is because that the descend degree of the first order inherent frequency relates not only to sealant failure size but also to failure position and process.
Inherent frequency/Hz
120 First order inherent frequency 100 80 60 40
1
2
3
4
5
6
--
Working condition
Fig.9 The first order inherent frequency under different working condition
4.3 Measure point analysis We can see from Table 6 that there is little difference between the test values of the first order inherent frequency at different measure point when the working condition is the same. This means that the accurate first order inherent frequency of HFSGCW can be obtained by any measure point. However, the frequency spectrum is susceptible to measure point. The farther the measure point from the edge, the smaller the vibration force, and the larger the proportion of the first order frequency amplitude in spectrogram. In this case, the peak frequency can be easily obtained. Fig.10 shows that the vibration force of measure point 1 is the maximum, closely followed by measure point 9, and then the measure point 17 and 25. Meanwhile, the amplitude of the first order frequency has a totally different trend. Therefore, the measure point must depart from the edge at a distance when the LDV is used to test the dynamic parameters of HFSGCW. The central point of the HFSGCW glass panel should be chosen for the test of the first order inherent frequency. In addition, the average value of three points at the central position is suggested to be the final value in order to decrease measurement errors.
0.03 -1
Magnitude/(mm·s )
Magnitude/(mm·s-1)
0.03
0.02 1 9 17 25
0.01
0.00
0.02
0.01
0.00
0
100
200 300 400 Frequency/Hz
1 9 17 25
500
60
80 100 120 Frequency/Hz
140
(a) 0-500 Hz (b) 50-150 Hz Fig.10 Spectrum signature of different measurement point under working condition 1
4.4 Sealant failure damage identification based on spectrum signature The intact condition of structure sealant has significant effect on spectrum signature under different working condition, especially for the measure point in the corner, for example the measure point 2 to 6. As shown in Fig.11, the proportion of first order inherent frequency amplitude in spectrogram is smaller when the structural sealant is intact (for example, working condition 1). The proportion has a substantial increase when the structural sealant is damaged (for example, working condition 4). Therefore, the first order inherent frequency test results of HFSGCW using LDV can be used for judging sealant failure preliminarily. Magnitude/(mm·s-1)
condition 1 point 2 condition 1 point 4 condition 1 point 6 condition 4 point 3 condition 4 point 5
0.009
0.0015
condition 1 point 3 condition 1 point 5 condition 4 point 2 condition 4 point 4 condition 4 point 6
Magnitude/(mm·s-1)
0.012
0.0012 0.0009
0.006
Condition 1 point 3 Condition 1 point 5 Condition 4 point 2 Condition 4 point 4 Condition 4 point 6
0.0006
0.003 0.000
Condition 1 point 2 Condition 1 point 4 Condition 1 point 6 Condition 4 point 3 Condition 4 point 5
0.0003
0
100
200 300 400 Frequency/Hz
500
0.0000 50
100 Frequency/Hz
(a) 0-500 Hz (b) 50-150 Hz Fig.11 The effect of sealant failure on the spectrum signature
150
4.5 Damage identification based on spectrum signature Fig.12 shows that when the structural sealant is intact or has slight damage, the frequency spectrum curve got by LDV has shark peak and smooth line, for example, the measure point 24, 25 and 26 under the working condition 1and 5. The frequency spectrum curves have no apparent main peak and fluctuate up and down when the structural sealant is seriously damaged, for example, the measure point 24, 25 and 26 under the working condition 6. At this moment, the first peak of frequency spectrum curve at frequency of 50Hz around should be identified as the first order inherent frequency which is consistent with the first order inherent frequency test results of DASP modal analysis. Therefore, the LDV measure points on HFSGCW should be increased or the modal analysis should be conducted when the frequency spectrum curve has the above characteristic in order to avoid the occurrence of serious damage. 0.030
0.018
Condition 5 point 25 Condition 6 point 25
0.012 0.006 0.000
0
100
200 300 400 Frequency/Hz
500
Condition 1 point 24 Condition 1 point 26 Condition 5 point 24 Condition 5 point 26 Condition 6 point 24 Condition 6 point 26
-1
0.024
Condition 1 point 25
Magnitude/(mm·s )
Magnitude/(mm·s-1)
0.0020 Condition 1 point 24 Condition 1 point 26 Condition 5 point 24 Condition 5 point 26 Condition 6 point 24 Condition 6 point 26
0.0015
Condition 1 point 25 Condition 5 point 25 Condition 6 point 25
0.0010 0.0005 0.0000
0
50 Frequency/Hz
100
(a) 0-500 Hz (b) 0-100 Hz Fig.12 Spectrum signature under different damage
5 Discussion Based on the research result in 3.2, the safety state of HFSGCW is closely related to the first order inherent frequency. The safety state of HFSGCW is divided into three levels, as shown in Table 7. Then, the safety state rapid evaluation model of HFSGCW is established according to LDV dynamic parameter, as shown in Fig.13.
Table 7 Safety state evaluation model of HFSGCW Safety levels A
Inherent frequency f f
Safety state Absolute safety state
B
f f f
Relative safety state
C
f f
Dangerous state
Solutions Regular management Strengthening management Replacement or Reinforcement
f f Absolute safe A
Relative Dangerous safe
B
C
Safety state
Fig.13 Safety state evaluation model based on first order inherent frequency Fig.13 shows that the key of the safety state rapid evaluation model is the critical value of the first order inherent frequency f and f . Because that the constrained boundary of HFSGCW is between four sides clamp supported and simply supported, the inherent frequency theoretical value of HFSGCW under four sides simply supported working condition is chosen for critical value f . Meanwhile, the f are given as 1.2f , where n is safety factor and a constant greater than 1. In this paper, the f 68.6Hz ，n=1.2， f 1.2f 82.3Hz 。The test results show that the HFSGCW under working condition 1, 2 and 3 is in absolute safety state, the HFSGCW under working condition 4 and 5 is in relative safety state, and the HFSGCW under working condition 6 is in dangerous state. It is important to know that safety state rapid evaluation model for HFSGCW is a conceptual model and the critical value of f and f change with practical
engineering. Meanwhile, the damage size and position also has a significant effect on the value of f and f . However, the safety state levels based on LDV dynamic parameters apply to all HFSGCW, making the operation, maintenances, management and safety detection easier. 6 Conclusions The safety state of HFSGCW is closely related to the first order inherent frequency obtained by LDV, and the results match well with that obtained by DASP. The safety state of HFSGCW becomes worse and worse with the decrease of first order inherent frequency. The measure point should be located the central place of HFSGCW glass panel. Therefore, the value of the first order inherent frequency is easily to be obtained, and the error can be decreased. The proportion of the first order inherent frequency in spectrogram is smaller when the structural sealant is intact, and the proportion significantly increases when the sealant failure is destroyed. When the structural sealant is in dangerous state, the frequency spectrum curves have no apparent main peak and fluctuate up and down. The safety state rapid evaluation model of HFSGCW is proposed in this paper on the basis of LDV dynamic parameter (first order inherent frequency). LDV has many advantages such as high precision, fast test speed, immunity to environment, remote, non-contact and so on, which makes the LDV has great prospect in the future safety detection work of HFSGCW. It also has great practical value for safety state detection of existing HFSGCW. Meanwhile, the difference quantification of this safety state rapid evaluation model is the emphasis for the next research work.
Acknowledgements This project has been supported by National Natural Science Foundation of China (Grant No. 41572274). Reference [1] Wang N., Ma J., Liu H.. Influence of Structural Sealant on Mechanical Behavior of Hidden Frame Curtain Wall [J]. Applied Mechanics and Materials, Vols.44-47(2011): pp 2534-2538. [2] Ma Q.. Reliability analysis of structural bonding of building glass curtain walls in our country[J].Adhesion,2016(3):61-65. (In Chinese) [3] Qing L., Cui H., Xing F., et al. Reasons for glass plate falling in hidden frame glass curtain wall[J]. China building waterproofing, 2013(17):18-20+29. (In Chinese) [4] Wu H., Zeng S., Li Z.. Study on safety evaluation method of glass curtain wall[J].Journal of natural disaters,2010,19(5):96-100. (In Chinese) [5] Liu J., Li J., Ding L.,et al.. Research and development in safe inspection and evaluation for existing building curtain walls[J]. Construction technology,2013,42(24):9-14+81. (In Chinese) [6] Efstathiades, C., et al., Application of neural networks for the structural health monitoring in curtain-wall systems. [7] Zhou, C., et al., Experimental Study on Dynamic Thermal Response of Building Attached Photovoltaic (BAPV) Curtain Wall System. Procedia Engineering, 2017. 205: 314-320. [8] Huang, B., et al., Seismic demand and experimental evaluation of the nonstructural building curtain wall: A review. Soil Dynamics and Earthquake Engineering, 2017. 100: 16-33. [9] Bedon C., Amadio C.. Numerical assessment of vibration control systems for multi-hazard design and mitigation of glass curtain walls. Journal of Building Engineering, 2018,15:1-13. [10] Amadio C., Bedon C.. Effect of circumferential sealant joints and metal supporting frames on the buckling behavior of glass panels subjected to in-plane shear loads[J]. Glass Structures & Engineering, 2016, 1(2):353-373. [11] Bedon C., Amadio C.. Exploratory numerical analysis of two-way straight cable-net façades subjected to air blast loads[J]. Engineering Structures, 2014, 79(79):276-289. [12] Bedon C., Belis J., Amadio C.. Structural assessment and lateral–torsional buckling design of
glass beams restrained by continuous sealant joints[J]. Engineering Structures, 2015, 102(-):214-229. [13] Bedon C., Amadio C. A Unified Approach for the Shear Buckling Design of Structural Glass Walls with Non-Ideal Restraints. American Journal of Engineering and Applied Sciences[J]. 2016,9(1): 64-78. [14] Chen Z., Luo Y., Gu J.. New damage detection method of structural silicone sealant in hidden frame supported glass curtain wall based on FFT power spectrum [J]. Sichuan building secience,2009, 35(2):104-107. (In Chinese) [15] Fang Z., Luo W.. Study on the damage detection of full-scale frme-concealed glass curtain-walls based on modal curvature[J].Value engineering,2017(20):89-93. (In Chinese) [16] Liu X.,Bao Y.,Song Y., et al.Safety evaluation of glass curtain walls by using dynamic method[J].China civil engineering journal,2009,42(12):11-15. (In Chinese) [17] Liu X.,Bao Y.. Safety evaluation for frame supported glass curtain wall based on natural frequency change[J].Journal of shenyang university of technology,2011,33(5):595-600. (In Chinese) [18] Chopra A. K.. Dynamics of structures [M]. New Jersey: Prentice Hall, 2000 [19] http://www.cnsealant.com/product/9.html
[20] http://www.81888682.com/Product-77.html Highlights 1) Damage of hidden-frame glass curtain wall is detected by laser doppler Vibrameter. 2) Sealant failure damage makes first order inherent frequency of curtain wall decrease. 3) Rapid evaluation model of curtain wall is built based on dynamic parameter. 4) Safety state of hidden-frame glass curtain wall is divided into three levels.
Graphical abstract
PII: DOI: Reference:
S2352-7102(18)30215-8 https://doi.org/10.1016/j.jobe.2018.04.030 JOBE475
To appear in: Journal of Building Engineering Received date: 23 February 2018 Revised date: 28 April 2018 Accepted date: 28 April 2018 Cite this article as: Zhide Huang, Mowen Xie, Jinhui Zhao, Yan Du and Hong-ke Song, Rapid Evaluation of Hidden Frame Supported Glass Curtain Wall Safety State Based on Remote Vibration Measurement, Journal of Building Engineering, https://doi.org/10.1016/j.jobe.2018.04.030 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Rapid Evaluation of Hidden Frame Supported Glass Curtain Wall Safety State Based on Remote Vibration Measurement Zhide Huang1,2, Mowen Xie1,*, Jinhui Zhao3, Yan Du1, Hong-ke Song1 1
School of Civil and Resource Engineering, University of Science and Technology Beijing, Beijing, 100083, China 2 School of Civil Engineering, Inner Mongolia University of science and technology, Baotou, Inner Mongolia, 014010, China 3 Shenzhen Taike test CO,LTD, Shenzhen, Guangdong, 518053, China Corresponding author. [email protected]
Abstract The vibration performance of simulation hidden frame supported glass curtain wall (HFSGCW) was tested using Laser Doppler Vibrometer (LDV) in this paper. The effect of silicon structural sealant on the first order inherent frequency of HFSGCW and the spectral characteristics got by LDV on different points were studied. Meanwhile, the test results of LDV were verified using traditional sensor (DASP modal analysis system) in order to evaluate the feasibility of LDV used for safety state evaluation of HFSGCW. The results show that the first order inherent frequency obtained by LDV matches well with DASP modal analysis results. The first order inherent frequency decreases with the increase of sealant failure, and increases significantly when the structural silicon sealant was completely destroyed. The safety state of HFSGCW was divided into three levels. Meanwhile, the safety state rapid evaluation model and key detection technologies of HFSGCW based on LDV was proposed.
Key words: Laser Doppler Vibrometer (LDV), Hidden frame supported glass curtain
wall (HFSGCW), Modal analysis, Safety state, Evaluation model
Main symbols HFSGCW-Hidden Frame Supported Glass Curtain Wall DASP-Data Acquisition & Signal Processing, a modal measure and analysis system produced by China Orient Institute of Noise & Vibration LDV-Laser Doppler Vibrameter SISO-Single Input Single Output
f DASP ,n -nth order modal frequency measured by DASP f LDV ,n -nth order modal frequency measured by LDV f n -nth order modal frequency
n -nth order modal damping ratio 1 Introdution Hidden frame supported glass curtain wall (HFSGCW) is light in mass, transparent, and relatively energy efficient, which is a kind of new technology product. The aluminum alloy outline border is removed and the glass panels are cohered on the metal framework through structural silicon sealant. The quality guarantee period of structural silicon sealant is usually 10 years [1,2], which means that the existing HFSGCWs built on 10 years ago are under challenges such as the aging of structural silicon sealant, the decrease of bonding force, the possibility of shedding and so on[3,4]. Meanwhile, the project quality field detection contents of existing curtain wall mainly focus on the appearance quality such as geometry size, coating film thickness, corrosion situation. The detection criterion can reflect the physical condition of HFSGCWs, but cannot reflect the safety state of HFSGCWs. Therefore, the prevention of glass falling off and decrease of casualty loss are urgently needed to be solved for HFSGCWs. The previous researches are mainly focused on the monolithic reliability
assessment of HFSGCW [5-9], and there is less result about the damage identification of curtain wall glass panel. Bendon and Amadio [10-13] studied the shear, lateral-torsional buckling of curtain wall glass panels restrained by different boundary condition. They gives three different restraint boundary conditions of glass curtain wall: 1) linear adhesive joints along the top and bottom edges only 2) supporting metal frames with interposed linear adhesive joints and 3) mechanical point-fixing connectors. Chen et al. [14] conducted the impulse response experiment on glass curtain wall and the experimental data was calculated using Gaussian and Lorentzian function. The relation between the propotion of FFT main peak frenquency to signal total power and the damage length of structural sealant was set up. However, this method was based on the mode of power spectral density and sealant failure length, and the application range of the model also needed to be determined. Fang et al. [15] analyzed the modal of curtain wall under different constraint using ANSYS finit element software. They proposed that the damage condition of structural sealant can be recognized through modal curvature change features. However, this method is based on the structural modal analysis and belongs to the follow-up work after the confirmation of safety state. The safety state of exposed frame glass curtain wall was simulated by Liu et al. [16, 17] through adjusting the bolt tightness degree of alloy shell frame. They also verified the feasibity of using inherent frequency to evaluate the tightness degree of curtain wall shell frame, and they built simple evaluation model based on two boundary conditions including four sides clamp support and simply support. They considered that the inherent frequency lower limit of curtain wall at work is the inherent frequency under four sides simply support. However, the conclusions do not contain the free boundary condition caused by local adhesive failure damage. Above all, evaluating the safety state using dynamic characteristics
has been done mainly based on numerical simulation and tradition modal testing method, and the researches are mainly targeted at exposed frame glass curtain wall. The related research about HFSGCW is rarely. Meanwhile, the tradition contacted sensor used for modal testing and analysis consume a mass of labor and time, so the practicability is heavily discounted in practical detection. The inherent frequency of HFSGCW under different working condition was tested through LDV and traditional sensor (DSAP) respectively in this paper. The research results will provide reference for safety state evaluating of existing HFSGCW. Meanwhile, the safety state evaluation model of HFSGCW was built and the safety state level was divided. 2 Vibration theory As an intrinsic characteristic, the structure vibration performance is closely related to boundary condition and physical property. The constraint of curtain wall shell frame to glass panel is reducing with the aging of structural sealant and the increment of service life. This means that the dynamic parameters change inevitably with the transformation of vibration theory boundary conditions, and this is the theoretical basis of curtain wall safety state evaluation. Curtain wall glass is typical thin-slab structure, and the lateral oscillation differential equation is [18]:
4w 4w 4w 4 2 w 0 x 4 x 2 y 2 y 4
（1）
Where
4
m 2 D
（2）
where is the inherent circular frequency of glass panel, rad/s; m is the mass per unit area of glass panel, kg/m2; D is the flexural rigidity of glass panel, N·m; a, b is the plan size of glass panel; the computational formula of flexural rigidity is:
D
Eh3 (1 2 ) 12
（3）
Where E is glass panel elasticity modulus; h is the glass panel thickness; is the glass panel Poisson ratio. The inherent circular frequency deduced from oscillatory differential equation is as follows. When the four sides of glass panel are clamp supported:
12
504 D 4 ( a 4 b 4 a 2b 2 ) 4 4 7 a ·b ·m
（4）
When the four sides of glass panel are simply supported:
1 2 (
1 1 D ) a 2 b2 m
（5）
The boundary condition of HFSGCW at work is between four sides clamp support and simply support, and the first order inherent frequency (f1, Hz)of the two boundary conditions respectively is as follows. When the four sides of glass panel are clamp supported:
f1
1 1 2 2
504 D 4 ( a 4 b 4 a 2b 2 ) 4 4 7 a ·b ·m
（6）
When the four sides of glass panel are simply supported:
f1
1 1 1 D ( ) 2 2 a 2 b2 m
（7）
3 Experimental programs 3.1 Instruments The vibration performance of HFSGCW is tested simultaneously using LDV (PDV-100, produced by Polytec Company, Germany) and DASP modal analysis system (produced by China Orient Institute of Noise&Vibration).
The working principle of LDV is Doppler Effect. When the vibrating object keeps way from the LDV, the wave length of reflected light elongates, and when the vibrating object is close to the LDV, the wave length of reflected light shortens. The LDV transmits HeNe laser beam to the object surface, and collect reflection light simultaneously. The vibration velocity of object is obtained by means of demodulating frequency shift signal based on Doppler Effect. The object vibration frequency domain curve is got through FFT and then the peak value is the object inherent frequency. Compared to traditional vibration sensor, the remote and non-contact properties of LDV give it the unique advantages in practical application, and the measurement accuracy far exceeds traditional contact sensor. Meanwhile, the LDV is not subject to environments. The LDV is show in Fig.1, and the working principle is shown in Fig.2. Table 1 shows the main technical parameters of LDV. As a traditional sensor, the result of DASP modal analysis system was used to verify the accurate of LDV. Fig.3 shows the set-up of DASP modal analysis system, and Table 2 shows the basic technical parameters of it.
Fig.1
LDV
Object Incident ray Reflected ray (a) Initial position
(b) The object come near, the wave length of the reflected ray shortens
(c) The object is away, the wave length of the reflected ray elongates
Fig.2 Measurement principle of LDV
Table 1 Technical parameters of LDV Frequency range Speed
Ranging scope 100 m
0.5Hz-22kHz
Curtain wall glass
Acceleration sensor
Exciting hammer
500 mm/s
Vibration signal
Signal collecting device
Resolution ratio 0.02 µm/(s·Hz0.5)
PC& DASP software package
Exciting signal
Fig.3 Set-up diagram of DASP modal analysis system
Type INV9822
Table 2 Technical parameters of the traditional sensor Sensitivity Frequency Range Resolution ratio 100 mv/g 0.5-8 kHz 50 g 0.002 m/s2
3.2 Raw materials The common tempered glass and single silicone structural sealant (MF899) [19] were used, and the parameters are shown in Table 3 and Table 4 respectively.
Side length, a/mm 600
State Pasty fluid
Table 3 Basic parameters of glass specimen Side length, Thickness Elasticity Density/(kg·m-2) b/mm /mm modulus/GPa 600 5 12.5 70
Color Black
Possion ratio, ν 0.24
Table 4 Properties of structural sealant Extrusion/s Shore hardness Tensile strength/MPa 1.8 43 2.1
3.3 Experimental design In order to simulate the frame support structure system of HFSGCW, the joist steel was fixed on the wall through anchor bolts, as shown in Fig.4 (a). The inner size of joist steel frame is 55cm×55cm, and the outside size is 69cm×69cm, as shown in Fig.4 (b). The curtain wall glass was pasted to joist steel frame using silicon structural sealant, as shown in Fig.4 (c) and Fig.4 (d). The width of the structural sealant is 2.5 cm and the thickness is 0.5 cm. The experimental photograph is shown in Fig.5 (a) and the corresponding measure point division is shown in Fig.5 (b). The glass was divided into thirty-six table cells and forty-nine measure points, and the reflector plate was pasted on the measure point. The DASP sensor was pasted on the ninth measure point using 502 glue [20].The standard working condition was in full adhesion, and the sealant failure was accomplished through cutting. The working condition in this paper was divided into six different situations on the basis of sealant failure, as shown in Fig.6. 70mm
60cm
69cm
Glue side
4.5mm
Anchor bolts 100mm
Steel frame 55cm
Sealant 69cm
60cm
Glass panel
55cm
7cm 7cm
Anchor side
(a)
(b)
(c)
(d)
Fig.4 Experimental apparatus. (a) Section dimension of steel frame; (b) Anchor side of steel frame; (c) Glue side of steel frame; (d) Experiment apparatus: steel frame ,sealant and glass panel
(a) Experimental photogragh (b) Table cell and measure point Fig.5 Glass curtain wall experimental photograph and measure point
27.5cm
Condition 1
Condition 2
Condition 3
40cm
Condition 4 Condition 5 Condition 6 Fig.6 Sealant failure illustration of different working conditions
3.4 Testing process The testing process was shown in Fig.7. Fig.7 shows that the modal analysis using DASP was conducted firstly, and then the dynamic test was done using LDV.
The DASP modal analysis system was based on SISO, and the ninth measure point was selected as the reference point. The variable time theory was used to sample. Three samples were conducted on every point. The sampling frequency is 51.2 kHz, and the variable-time multiple and the sensor frequency is 32 and 1600 Hz respectively. The analytical frequency is 800 Hz. The time-domain signal was translated into rumble spectrum signal through FFT. The sampling point was set as 8192. After that, frequency-response function calculation was done, and the average value was selected to be modal order. The fitting was done on the basis of complex mode and single degree of freedom in order to get the modal parameters and modal shape. The reflector plate was used to increase reflected signal in LDV test. The artificial excitation was chosen to trigger object. The sampling frequency is 1200 Hz, the bandwidth is 500 Hz, and the sample time is 6.4 s. The forty-nine points were all tested under every working condition, and the average first order frequency of all points was selected as the final first order inherent frequency. Condition 1
Modal test （DASPSISO）
LDV test
Results analysis
Cutting adhesive Modal test （DASPSISO）
Condition 3
……
Cutting adhesive LDV test
Clean the lab
Cutting adhesive
LDV test
Condition 6
Finish the test
Modal test （DASPSISO）
Modal test （DASPSISO）
LDV test
Cutting adhesive Condition 2
Fig.7 Testing process
4 Result and analysis 4.1 Comparative analysis of test results obtained by LDV and DASP Table 5 shows the test results of first order inherent frequency of six different working conditions. The first order inherent frequency obtained by LDV is in accordance with the results tested by DASP, which illustrate that the accurate measurement of dynamic parameter can be realized by LDV. Table 6 shows the discreteness of the LDV first order inherent frequency. The standard deviation of the first to fifth working condition is ±0.5 Hz, and the standard deviation of the sixth working condition is 1.67 Hz, which also shows that the LDV can realize the accurate measurement of HFSGCW dynamic parameter.
Table 5 Test results of first order frequencies of different working condition (Hz) f LDV f DASP f DASP f LDV Working condition 1 94.26 94.24 -0.02 2 90.33 90.61 0.28 3 88.35 89.13 0.78 4 80.38 79.43 -0.95 5 78.28 78.07 -0.21 6 49.71 49.95 0.24
Table 6 Discreteness of the test results (Hz) Working condition 1 2 3 4 5 6
Maximum
Minimum
Difference
94.84 91.56 89.69 80.16 78.59 53.59
93.16 89.06 87.34 78.44 76.25 46.72
1.68 2.5 2.35 1.72 2.34 6.87
Standard deviation 0.33 0.51 0.39 0.43 0.41 1.67
Fig.8 The first order vibration modal shape of HFSGCW
The vibration modal shape obtained by DASP was shown in Fig.8, in which the legend value is normalized by the maximum displacement. With the change of working condition, the modal shape has moving toward the sealant failure direction. However, because that structural sealant has not been fully broken, the cutting damage can only weaken boundary constraint, but cannot eliminate it. Therefore, the deviation of modal shape is not obvious between working condition 2 and 3. Similarly, this phenomenon occurs between working condition 4 and 5. 4.2 Sealant failure analysis As shown in Table 5, the first order inherent frequency of HFSGCW decrease with the increase of sealant failure, indicating that the safety state of HFSGCW can be determined by first order inherent frequency. Fig.9 shows that the sealant failure increment is the same from working condition 3 to 4 and from working condition 4 to 5, but the first order frequency range for the former is larger than that for the later. This is because that the descend degree of the first order inherent frequency relates not only to sealant failure size but also to failure position and process.
Inherent frequency/Hz
120 First order inherent frequency 100 80 60 40
1
2
3
4
5
6
--
Working condition
Fig.9 The first order inherent frequency under different working condition
4.3 Measure point analysis We can see from Table 6 that there is little difference between the test values of the first order inherent frequency at different measure point when the working condition is the same. This means that the accurate first order inherent frequency of HFSGCW can be obtained by any measure point. However, the frequency spectrum is susceptible to measure point. The farther the measure point from the edge, the smaller the vibration force, and the larger the proportion of the first order frequency amplitude in spectrogram. In this case, the peak frequency can be easily obtained. Fig.10 shows that the vibration force of measure point 1 is the maximum, closely followed by measure point 9, and then the measure point 17 and 25. Meanwhile, the amplitude of the first order frequency has a totally different trend. Therefore, the measure point must depart from the edge at a distance when the LDV is used to test the dynamic parameters of HFSGCW. The central point of the HFSGCW glass panel should be chosen for the test of the first order inherent frequency. In addition, the average value of three points at the central position is suggested to be the final value in order to decrease measurement errors.
0.03 -1
Magnitude/(mm·s )
Magnitude/(mm·s-1)
0.03
0.02 1 9 17 25
0.01
0.00
0.02
0.01
0.00
0
100
200 300 400 Frequency/Hz
1 9 17 25
500
60
80 100 120 Frequency/Hz
140
(a) 0-500 Hz (b) 50-150 Hz Fig.10 Spectrum signature of different measurement point under working condition 1
4.4 Sealant failure damage identification based on spectrum signature The intact condition of structure sealant has significant effect on spectrum signature under different working condition, especially for the measure point in the corner, for example the measure point 2 to 6. As shown in Fig.11, the proportion of first order inherent frequency amplitude in spectrogram is smaller when the structural sealant is intact (for example, working condition 1). The proportion has a substantial increase when the structural sealant is damaged (for example, working condition 4). Therefore, the first order inherent frequency test results of HFSGCW using LDV can be used for judging sealant failure preliminarily. Magnitude/(mm·s-1)
condition 1 point 2 condition 1 point 4 condition 1 point 6 condition 4 point 3 condition 4 point 5
0.009
0.0015
condition 1 point 3 condition 1 point 5 condition 4 point 2 condition 4 point 4 condition 4 point 6
Magnitude/(mm·s-1)
0.012
0.0012 0.0009
0.006
Condition 1 point 3 Condition 1 point 5 Condition 4 point 2 Condition 4 point 4 Condition 4 point 6
0.0006
0.003 0.000
Condition 1 point 2 Condition 1 point 4 Condition 1 point 6 Condition 4 point 3 Condition 4 point 5
0.0003
0
100
200 300 400 Frequency/Hz
500
0.0000 50
100 Frequency/Hz
(a) 0-500 Hz (b) 50-150 Hz Fig.11 The effect of sealant failure on the spectrum signature
150
4.5 Damage identification based on spectrum signature Fig.12 shows that when the structural sealant is intact or has slight damage, the frequency spectrum curve got by LDV has shark peak and smooth line, for example, the measure point 24, 25 and 26 under the working condition 1and 5. The frequency spectrum curves have no apparent main peak and fluctuate up and down when the structural sealant is seriously damaged, for example, the measure point 24, 25 and 26 under the working condition 6. At this moment, the first peak of frequency spectrum curve at frequency of 50Hz around should be identified as the first order inherent frequency which is consistent with the first order inherent frequency test results of DASP modal analysis. Therefore, the LDV measure points on HFSGCW should be increased or the modal analysis should be conducted when the frequency spectrum curve has the above characteristic in order to avoid the occurrence of serious damage. 0.030
0.018
Condition 5 point 25 Condition 6 point 25
0.012 0.006 0.000
0
100
200 300 400 Frequency/Hz
500
Condition 1 point 24 Condition 1 point 26 Condition 5 point 24 Condition 5 point 26 Condition 6 point 24 Condition 6 point 26
-1
0.024
Condition 1 point 25
Magnitude/(mm·s )
Magnitude/(mm·s-1)
0.0020 Condition 1 point 24 Condition 1 point 26 Condition 5 point 24 Condition 5 point 26 Condition 6 point 24 Condition 6 point 26
0.0015
Condition 1 point 25 Condition 5 point 25 Condition 6 point 25
0.0010 0.0005 0.0000
0
50 Frequency/Hz
100
(a) 0-500 Hz (b) 0-100 Hz Fig.12 Spectrum signature under different damage
5 Discussion Based on the research result in 3.2, the safety state of HFSGCW is closely related to the first order inherent frequency. The safety state of HFSGCW is divided into three levels, as shown in Table 7. Then, the safety state rapid evaluation model of HFSGCW is established according to LDV dynamic parameter, as shown in Fig.13.
Table 7 Safety state evaluation model of HFSGCW Safety levels A
Inherent frequency f f
Safety state Absolute safety state
B
f f f
Relative safety state
C
f f
Dangerous state
Solutions Regular management Strengthening management Replacement or Reinforcement
f f Absolute safe A
Relative Dangerous safe
B
C
Safety state
Fig.13 Safety state evaluation model based on first order inherent frequency Fig.13 shows that the key of the safety state rapid evaluation model is the critical value of the first order inherent frequency f and f . Because that the constrained boundary of HFSGCW is between four sides clamp supported and simply supported, the inherent frequency theoretical value of HFSGCW under four sides simply supported working condition is chosen for critical value f . Meanwhile, the f are given as 1.2f , where n is safety factor and a constant greater than 1. In this paper, the f 68.6Hz ，n=1.2， f 1.2f 82.3Hz 。The test results show that the HFSGCW under working condition 1, 2 and 3 is in absolute safety state, the HFSGCW under working condition 4 and 5 is in relative safety state, and the HFSGCW under working condition 6 is in dangerous state. It is important to know that safety state rapid evaluation model for HFSGCW is a conceptual model and the critical value of f and f change with practical
engineering. Meanwhile, the damage size and position also has a significant effect on the value of f and f . However, the safety state levels based on LDV dynamic parameters apply to all HFSGCW, making the operation, maintenances, management and safety detection easier. 6 Conclusions The safety state of HFSGCW is closely related to the first order inherent frequency obtained by LDV, and the results match well with that obtained by DASP. The safety state of HFSGCW becomes worse and worse with the decrease of first order inherent frequency. The measure point should be located the central place of HFSGCW glass panel. Therefore, the value of the first order inherent frequency is easily to be obtained, and the error can be decreased. The proportion of the first order inherent frequency in spectrogram is smaller when the structural sealant is intact, and the proportion significantly increases when the sealant failure is destroyed. When the structural sealant is in dangerous state, the frequency spectrum curves have no apparent main peak and fluctuate up and down. The safety state rapid evaluation model of HFSGCW is proposed in this paper on the basis of LDV dynamic parameter (first order inherent frequency). LDV has many advantages such as high precision, fast test speed, immunity to environment, remote, non-contact and so on, which makes the LDV has great prospect in the future safety detection work of HFSGCW. It also has great practical value for safety state detection of existing HFSGCW. Meanwhile, the difference quantification of this safety state rapid evaluation model is the emphasis for the next research work.
Acknowledgements This project has been supported by National Natural Science Foundation of China (Grant No. 41572274). Reference [1] Wang N., Ma J., Liu H.. Influence of Structural Sealant on Mechanical Behavior of Hidden Frame Curtain Wall [J]. Applied Mechanics and Materials, Vols.44-47(2011): pp 2534-2538. [2] Ma Q.. Reliability analysis of structural bonding of building glass curtain walls in our country[J].Adhesion,2016(3):61-65. (In Chinese) [3] Qing L., Cui H., Xing F., et al. Reasons for glass plate falling in hidden frame glass curtain wall[J]. China building waterproofing, 2013(17):18-20+29. (In Chinese) [4] Wu H., Zeng S., Li Z.. Study on safety evaluation method of glass curtain wall[J].Journal of natural disaters,2010,19(5):96-100. (In Chinese) [5] Liu J., Li J., Ding L.,et al.. Research and development in safe inspection and evaluation for existing building curtain walls[J]. Construction technology,2013,42(24):9-14+81. (In Chinese) [6] Efstathiades, C., et al., Application of neural networks for the structural health monitoring in curtain-wall systems. [7] Zhou, C., et al., Experimental Study on Dynamic Thermal Response of Building Attached Photovoltaic (BAPV) Curtain Wall System. Procedia Engineering, 2017. 205: 314-320. [8] Huang, B., et al., Seismic demand and experimental evaluation of the nonstructural building curtain wall: A review. Soil Dynamics and Earthquake Engineering, 2017. 100: 16-33. [9] Bedon C., Amadio C.. Numerical assessment of vibration control systems for multi-hazard design and mitigation of glass curtain walls. Journal of Building Engineering, 2018,15:1-13. [10] Amadio C., Bedon C.. Effect of circumferential sealant joints and metal supporting frames on the buckling behavior of glass panels subjected to in-plane shear loads[J]. Glass Structures & Engineering, 2016, 1(2):353-373. [11] Bedon C., Amadio C.. Exploratory numerical analysis of two-way straight cable-net façades subjected to air blast loads[J]. Engineering Structures, 2014, 79(79):276-289. [12] Bedon C., Belis J., Amadio C.. Structural assessment and lateral–torsional buckling design of
glass beams restrained by continuous sealant joints[J]. Engineering Structures, 2015, 102(-):214-229. [13] Bedon C., Amadio C. A Unified Approach for the Shear Buckling Design of Structural Glass Walls with Non-Ideal Restraints. American Journal of Engineering and Applied Sciences[J]. 2016,9(1): 64-78. [14] Chen Z., Luo Y., Gu J.. New damage detection method of structural silicone sealant in hidden frame supported glass curtain wall based on FFT power spectrum [J]. Sichuan building secience,2009, 35(2):104-107. (In Chinese) [15] Fang Z., Luo W.. Study on the damage detection of full-scale frme-concealed glass curtain-walls based on modal curvature[J].Value engineering,2017(20):89-93. (In Chinese) [16] Liu X.,Bao Y.,Song Y., et al.Safety evaluation of glass curtain walls by using dynamic method[J].China civil engineering journal,2009,42(12):11-15. (In Chinese) [17] Liu X.,Bao Y.. Safety evaluation for frame supported glass curtain wall based on natural frequency change[J].Journal of shenyang university of technology,2011,33(5):595-600. (In Chinese) [18] Chopra A. K.. Dynamics of structures [M]. New Jersey: Prentice Hall, 2000 [19] http://www.cnsealant.com/product/9.html
[20] http://www.81888682.com/Product-77.html Highlights 1) Damage of hidden-frame glass curtain wall is detected by laser doppler Vibrameter. 2) Sealant failure damage makes first order inherent frequency of curtain wall decrease. 3) Rapid evaluation model of curtain wall is built based on dynamic parameter. 4) Safety state of hidden-frame glass curtain wall is divided into three levels.
Graphical abstract