CN101294891B - A method for detecting loose glass curtain walls and predicting fall risk - Google Patents

Abstract

A method for detecting the looseness of a glass curtain wall and predicting the risk of falling. The steps are: 1) determining the reference frequency range of the glass according to the parameters of the glass plate used in the glass curtain wall to be tested; 2) performing a laboratory simulation test on the same glass plate, and measuring Find out the corresponding natural frequencies under different fixing conditions, and obtain _the measurable frequency range _ωlower , _ωupper and loosening frequency _ωloose in the reference frequency range _; The difference between ω _looseness is used as the safe zone and dangerous zone for evaluation and classification; 3) On-site vibration signal sampling and detection of glass curtain wall glass to obtain the measured frequency of the glass curtain wall; 4) Comparing the field measured frequency value with the natural frequency classification, the obtained The safety and reliability level of curtain wall glass in this service state. The invention provides a convenient and simple non-destructive testing method for the glass industry and ensures the safety and reliability of glass products, especially glass curtain walls, during use.

Description

A method for detecting loose glass curtain walls and predicting fall risk

technical field

The invention relates to a non-destructive on-line detection technology for building curtain walls, in particular to a method for testing the safety and reliability of curtain wall glass, which uses the method of testing the natural frequency of curtain wall glass combined with mechanics to perform non-destructive online reliability testing on glass curtain walls, thereby predicting Risk of glass curtain wall loosening and falling.

Background technique

Since the 1980s, large and medium-sized cities in my country have successively built a large number of glass curtain wall buildings. Most of these buildings are located in bustling urban areas, and any cracking or falling accident of curtain wall glass may cause disastrous consequences. In recent years, more and more potential safety hazards of curtain wall glass have attracted the attention of many experts and the general public. During the ten or twenty years of extensive use of curtain wall glass, the various performances of curtain wall glass as an integrated structure and function have been continuously degraded and attenuated, and there are generally hidden safety hazards in the glass curtain walls currently in service. The silicone structural sealant used as a fixed adhesive may age over time, and even crack and fall off in severe cases. Especially for the hidden frame glass curtain wall that is commonly used now, since this type of curtain wall glass has no outer frame, it is completely glued to the surface of the aluminum material, and it needs to effectively resist wind load, self-weight load, thermal expansion and contraction, earthquake for a long time Therefore, once the structural sealant has problems, it is extremely dangerous. The looseness of frame supports and point-supported curtain walls also causes harm. The looseness of curtain walls not only affects the airtightness and thermal insulation performance of the room, but is even more dangerous. It may lead to catastrophic falling of high-altitude glass curtain walls. The curtain wall glass falling accident has caused serious disasters to the society.

So far, there is no effective way to evaluate and determine the safety, reliability, service life and durability of large glass during service, which is a big problem in the use of curtain wall glass.

Whether it is the design unit or the user unit of the building structure, it is very important and urgent to ensure the reliability of the curtain wall glass. For the glass industry and construction industry, the annual cost of building curtain wall glass is as high as hundreds of millions of yuan. It is obviously a major loss to replace all the expired curtain wall glass, but if safety inspection is not done, every time a disaster occurs, its economic The loss cannot be measured with specific data. Therefore, researching new methods for non-destructive on-line reliability testing of glass components, detecting and monitoring the health status and safety and reliability of glass curtain walls in service are of great importance for ensuring the safety of people's lives and property and promoting the development of glass deep processing and other industries significance.

Contents of the invention

The purpose of the present invention is to provide a method for detecting the looseness of glass curtain walls and predicting the risk of falling. In view of the above problems, the present invention provides a non-destructive online reliability testing technology for glass curtain walls using the combination of vibration diagnosis principle and mechanics.

The method for detecting loose glass curtain wall and predicting the risk of falling of the present invention adopts the following steps:

1) According to the parameters of the glass plate used in the glass curtain wall to be tested, determine the glass reference frequency range;

2) Determination of safety and reliability evaluation level: Carry out laboratory simulation tests on the same glass plate, measure the corresponding natural frequencies under different fixing conditions, and obtain the measurable frequency range ω _lower , ω _upper and loose frequency within the reference frequency range _ωloose ; the difference between the two extreme values _ωup and _ωdown of the measurable frequency range and the loosening frequency _ωloose is used as the safety interval and the dangerous interval for evaluation and classification;

3) On-site sampling test: use the corresponding excitation device and vibration pickup device to sample and detect the vibration signal of the glass curtain wall glass to obtain the measured frequency of the glass curtain wall;

4) Compare the measured frequency value measured on site in step 3) with the natural frequency classification in step 2), and obtain the safety and reliability level of the curtain wall glass in this service state according to the data comparison result.

Wherein, described step 1) adopts theoretical analysis method, calculates the lower limit value of reference frequency by formula (1):

${\mathrm{<span\; class="notranslate">\; \&omega;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 504</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; D.</span>}}{{\mathrm{<span\; class="notranslate">\; a</span>}}^{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; b</span>}}^{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; m</span>}}}<span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; a</span>}}^{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; b</span>}}^{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 4</span>}}{\mathrm{<span\; class="notranslate">\; 7</span>}}{\mathrm{<span\; class="notranslate">\; a</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; b</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

The upper limit of the reference frequency is calculated by formula (2):

$\mathrm{<span\; class="notranslate">\; \&omega;</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; a</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; b</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; )</span>\sqrt{\frac{\mathrm{<span\; class="notranslate">\; D.</span>}}{\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; m</span>}}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

-每单位面积的玻璃质量，a-玻璃长度，b-玻璃宽度；其中a和b为测量值，

根据被测试样材质从手册中查询或从幕墙安装原始数据中获得，弯曲刚度D的表达式为：Among them: ω-natural frequency of glass, D-bending stiffness of tested sample,

- glass mass per unit area, a - glass length, b - glass width; where a and b are measured values,

According to the material of the sample to be tested from the manual or obtained from the original data of the curtain wall installation, the expression of the bending stiffness D is:

D＝Eh ³ /12(1-υ ² ) (3)

Among them: E-Young's modulus of glass material; h-glass thickness; υ-Poisson's ratio of glass material.

Step 2) The evaluation is classified into four points: the loose frequency ω _loose is used as the standard dividing line for the safety and reliability of glass curtain walls, and the lower limit value ω _lower and ω _loose interval of the measurable frequency range are equally divided into two sections, starting from the lower limit The _lower value of ω to _{the loose} value of ω corresponds to the level of looseness and shedding and the level of hidden dangers; divide the interval between ω _loose and the upper limit value ω of the measurable frequency range _into two sections, and correspond in turn from the ω _loose value _to the upper limit value ω To use the security level and to use the reliable level.

Step 2) The evaluation is graded as another simplified quartile: the _lower limit ω and the upper limit ω of the reference frequency are equally _divided into four sections, and the values are divided into loose and falling off, hidden dangers, safe use and Use four levels of reliability.

In the above method, the upper limit of the theoretical glass reference frequency range and the measurable frequency range of the actual measured value corresponds to the four-sided fixing method of the glass, and the lower limit corresponds to the four-sided simple support of the glass fixing method.

In the above method, the evaluation standard of step 4) is: when the actual measured frequency results are similar in the standard safe range, the curtain wall glass structure can be considered safe; when it falls in the dangerous range, the structure is considered unsafe and it is recommended to replace Or take steps to strengthen its structure.

By adopting the technical solution of the invention, a convenient and simple non-destructive testing method can be provided for the glass industry, which ensures the safety and reliability of glass products during use. For glass enterprises and glass application units, it can reduce the cost of production and testing, and save the cost of glass product quality inspection; for construction units, it provides a simple and effective method for testing the construction quality of curtain wall glass, and the test cost is relatively low. Low, to avoid the occurrence of safety accidents; for glass users, the present invention provides a test method to ensure safe use of products.

Description of drawings

Fig. 1 is a schematic diagram of the working principle of the present invention;

Fig. 2 is a flow chart of the detection process of the present invention;

Fig. 3 is the spectrogram (corresponding fundamental frequency is 370Hz) of four sides fastening lower glass plate in the detection example of the present invention;

Fig. 4 is the spectrogram (corresponding fundamental frequency is 230Hz) of four sides loose lower glass plate in the detection example of the present invention;

Fig. 5 is the relationship curve between different boundary tightness and glass fundamental frequency and the division of safety levels in the detection example of the present invention.

Detailed ways

The present invention first needs to determine the relationship between the fundamental frequency (lowest natural frequency) of the glass curtain wall and the safety and reliability of the structure and the law of damage evolution. The basic principle is to determine the natural frequency of the glass curtain wall vibrating under certain support conditions through acoustic resonance or laser vibration measurement. The relationship between natural frequency and member stiffness is used to evaluate its structural reliability.

For a large service component, such as a four-sided clamped plate glass, its natural frequency is affected by its size, mass and stiffness. For a glass curtain wall of known size, the natural frequency can be considered to vary with its stiffness. When its four sides are loosened, or the glass curtain wall is damaged, its overall stiffness will decrease, and its natural frequency will also decrease. Therefore, the measured natural frequency can be used to evaluate whether the glass curtain wall is damaged or loose, thus forming a new method for non-destructive online testing of the safety of large glass components. There are multiple methods for measuring the natural frequency of the glass curtain wall, and the reliability of the measured frequency can be verified by comparing them with each other. The present invention mainly adopts modal analysis (experimental modal analysis and finite element analysis), acoustic induction vibration measurement and resonance method Several methods are used to determine the natural frequency.

A method for detecting the looseness of the glass curtain wall and predicting the risk of falling of the present invention is described as follows below:

The natural frequency of the glass curtain wall changes with the quality of the component, the degree of clamping and the degree of damage. Therefore, the present invention evaluates whether the component is damaged or loose by the measured natural frequency, so as to test the safety of large glass components on-line without damage. The relative method can be used to evaluate the natural frequency comparison of the glass curtain wall under different support tightness states, that is, first determine the natural frequency under the four-sided fastening state, and then compare the measured frequency with it. The greater the difference, the greater the risk probability. The frequency (also called reference frequency) under different fixed states can be obtained by theoretical calculation or finite element calculation; the frequency measured by a curtain wall with the same support and size and known safety can also be used as the reference frequency.

The following steps can be used to detect the looseness of the glass curtain wall and predict the risk of falling (see Figure 1 and Figure 2):

1) Determine the reference frequency range: Obtain the size of the glass curtain wall structure to be measured, which can be obtained from the original data at the time of installation, or sampled and measured. If the same style of glass curtain wall is installed, the reference frequency of a piece of glass can be calculated.

Theoretical analysis method: The fixing methods of glass curtain walls are generally divided into two types, the four-sided simply supported fixing method and the four-sided fixed supported fixing method. The glass in the four-sided fixed support method is firm, while the glass in the four-sided simply supported fixed method is loose. The state of the curtain wall glass in general service status should be between the four-sided simply supported and the four-sided fixed support. For the vibration fundamental frequency of the four-sided simply supported and fixedly supported rectangular thin plate, there are corresponding accurate analytical expressions in theory.

When the glass curtain wall is simply supported on four sides, its natural frequency is calculated by formula (1), which is the lower limit of the reference frequency:

${\mathrm{<span\; class="notranslate">\; \&omega;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 504</span>}<span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; D.</span>}}{{\mathrm{<span\; class="notranslate">\; a</span>}}^{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; b</span>}}^{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; m</span>}}}<span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; a</span>}}^{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; b</span>}}^{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 4</span>}}{\mathrm{<span\; class="notranslate">\; 7</span>}}{\mathrm{<span\; class="notranslate">\; a</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; b</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

When the glass is fixed in a four-sided way, its natural frequency is calculated by formula (2), which is the upper limit of the reference frequency:

$\mathrm{<span\; class="notranslate">\; \&omega;</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; a</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; b</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; )</span>\sqrt{\frac{\mathrm{<span\; class="notranslate">\; D.</span>}}{\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; m</span>}}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

-每单位面积的玻璃质量，a-玻璃长度，b-玻璃宽度；其中a和b为测量值，根据被测试样材质从手册中查询或从幕墙安装原始数据中获得，弯曲刚度D的表达式为：In formula (1) and formula (2): ω-natural frequency of glass, D-bending stiffness of tested sample,

- glass mass per unit area, a - glass length, b - glass width; where a and b are measured values, According to the material of the sample to be tested from the manual or obtained from the original data of the curtain wall installation, the expression of the bending stiffness D is:

D＝Eh ³ /12(1-υ ² ) (3)

Among them: E-Young's modulus of glass material; h-glass thickness; υ-Poisson's ratio of glass material.

Through the calculation of formula (1) and formula (2), it can be known that the natural frequency of the glass to be tested should be in the value range _between the upper limit value ω and the _lower limit value ω of the reference frequency.

Finite element analysis method: The finite element model needs to be corrected and verified by theoretical solutions and experiments, and finally obtain a finite element model that can reflect the actual situation. The corrected model can be used to calculate the natural frequency of glass curtain wall panels under different support conditions and support tightness.

2) Determination of the safety and reliability evaluation level: it can be determined comprehensively by using the test method and the finite element method. During the test, first test the curtain wall glass of the same size in the laboratory, within the reference frequency range determined in step 1), give the corresponding natural frequencies under different fixing conditions, and the fixing conditions can be divided into fastening (corresponding to ω _Up ), loose (corresponding to ω _loose ), falling off (corresponding to ω _down ) three levels. During finite element analysis, the natural frequency of glass curtain wall panels under different support conditions and support tightness can be calculated through the revised model. According to the test data or finite element analysis data, the relationship between the looseness of the glass plate and the natural frequency is finally obtained, and the safe range and dangerous range of the natural frequency of the glass curtain wall are established.

Evaluation Grading Method:

Quartering method: Divide the difference _between the upper limit value ω and the _lower limit value ω of the reference frequency of four-sided simple support and four-sided fixed support into four areas, among which the natural frequency ω _loose corresponding to the glass curtain wall can be used as the glass The standard dividing line for the safety and reliability of curtain walls. When the measured frequency is lower than this frequency, it is considered that the glass curtain wall has a safety hazard. When the measured frequency is higher than this frequency, it can be considered that the glass curtain wall is safe to use. When divided into four quarters, the frequency of the interval from _ωlower to _ωloose is divided into two sections. The corresponding frequency interval from _ωlower to _ωloose describes the use status of the glass curtain wall as loose and falling off and hidden dangers. The loosening and falling off of the glass curtain wall must be carried out. Replacement or reinforcement, there are potential safety hazards, it is considered that the glass curtain wall needs to be reinforced or repaired. Similarly, divide _ωloose to ωup _into two intervals, and from _ωloose to _ωup are respectively safe and reliable in use. The safety of use means that the glass curtain wall is in good condition and does not need maintenance and reinforcement, and the glass curtain wall is considered reliable in use. The curtain wall is in excellent condition and can continue to be used safely and reliably for a long time. For the method of dividing frequency intervals, refer to the specific example shown in FIG. 5 .

Another quartering method can be used to divide the upper limit value ω _and lower limit value ω of the reference frequency _into four segments equally, and divide them into four levels according to the value from small to large: loose and falling off, hidden danger, safe to use and reliable to use. In this division method, based on experience or finite element simulation _, it is known that _{the loose} position of ω is usually the middle position _{between the upper} limit value of ω and the _lower limit value ω.

3) On-site sampling test, select the corresponding excitation device and vibration pickup device, sample the vibration signal of the glass, and use the amplifier to amplify the signal and send it to the signal processing device. Finally, through computer software analysis, the measured natural frequency of the glass curtain wall is obtained.

4) Compare the measured frequency value measured on site with the natural frequency classification in step 2), and obtain the safety and reliability level of the curtain wall glass in this service state according to the data comparison result. When the actual measured frequency results are similar in the standard safe range, the curtain wall glass structure can be considered safe; when it falls in the dangerous range, the structure is considered unsafe, and it is recommended to replace or take measures to strengthen its structure.

The specific implementation route of the reliability evaluation technology of the present invention and the work flow of glass reliability evaluation equipment are shown in Figure 1 and Figure 2 .

The present invention will be described in detail below in conjunction with specific embodiments.

Example 1: Laboratory simulation of safety testing of different boundary-supported glass curtain wall structures

1) Preparation of glass samples: 300×300×4mm ordinary soda-lime silicate glass was used in this test, and the glass surface was cleaned before the test;

2) The measured glass size and material parameters on site are a=300mm, b=300mm, h=4mm, E=70GPa (elastic modulus), v=0.24 (Poisson's ratio), $\stackrel{\&OverBar;}{m}=10\mathrm{kg}/m^2.$ Calculated according to the analytical expressions of formula (1) and formula (2), the natural frequency value of the analytical solution of the tested glass in the fixed and simply supported state can be obtained (see Table 1); or the fixed support can be obtained according to the finite element analysis method and the natural frequency values of the finite element solution in the simply supported state (see Table 1). From the calculated natural frequency, it can be obtained that the frequency distribution range of the tested glass should be 216-398Hz.

3) Place the prepared glass sample on a 280×280mm square steel bottom frame, and cover the upper end with a square frame of the same size. The middle of the two frames is fixed with bolts, and the glass and the frame are supported by elastic rubber. The structure is modeled on an ordinary curtain wall structure, and the stiffness of the entire structure is controlled by adjusting the tightness of the bolts between the two frames to simulate the loosening of the glass curtain wall structure in the on-site monitoring. The simulation is classified into fastening, semi-fastening, and loosening and four levels of shedding, see Table 1.

4) Adjust the tightness of the bolts in the above structure from tight to loose, and obtain the natural frequency of the glass under different boundary tightness conditions through dynamic tests. The test data are listed in Table 1.

The test equipment adopts DLF-3 dual-channel filter integration amplifier produced by Dongfang Vibration and Noise Technology Research Institute, INV38V intelligent signal acquisition and processing analyzer and its supporting signal analysis software. See Figure 3 for the frequency spectrum of the glass obtained in this test under the condition of fastening, and Figure 4 for the frequency spectrum of the glass under the loose condition; from the frequency spectrum Figure 3, it can be seen that the corresponding natural frequency in the fastening state is 370Hz, and it can be directly shown in Figure 4 The natural frequency corresponding to the read loose state is 230Hz.

5) Safety grading: According to the frequency corresponding to the tightness of the boundary fixing, the frequency division interval of the safety level of the use state of the piece of glass is shown in Figure 5.

Table 1 The natural frequency and safety level division of the glass plate under different edge fittings

It can be seen from Table 1 and Figure 5 that the fundamental frequency (measured natural frequency) of the glass plate is between about 10% lower than the fundamental frequency corresponding to the four-sided fixed support and higher than the four-sided simple support (due to the fact that the boundary of the glass is fixed It is impossible to be completely supported by four sides or simply supported by four sides, so the frequency range which is about 10% away from the theoretical frequency of fixed or simply supported by four sides cannot be measured). And as the bolts get looser, the fundamental frequency decreases. The experiment in this example is based on the frequency corresponding to the bolts starting to loosen (the fundamental frequency corresponding to this test is 300Hz). When the measured frequency is lower than this frequency, it can be considered that the four sides of the glass plate are loose and the curtain wall structure is Safety hazard or risk of falling off. And when the measured frequency is higher than this frequency, it can be considered that the four sides of the glass plate are not loose, and the curtain wall structure is safe and reliable to use.

Example 2: On-site glass curtain wall detection and safety level evaluation

Project introduction: The curtain wall of a certain building is of exposed frame structure, and the glass panels are embedded in the aluminum frame. It was completed in August 2000. It is learned that the curtain wall glass is ordinary flat glass, the size of the glass is: 1415mm×1860mm×6mm, the elastic modulus of the glass is 72GPa, the Poisson’s ratio is 0.24, and the density is 2500kg/m ³ .

Evaluation standard division: Calculated according to the analytical expressions of formula (1) and formula (2), the corresponding frequencies of the single glass plate of the curtain wall under the condition of fixed support and simple support are respectively 22Hz and 11.8Hz. With the same method of embodiment steps 3) and 4), the same glass plate was tested in the laboratory, and the measurable frequency range was obtained between 13～20Hz, and the loosening frequency was 15.5Hz, and the loosening frequency was used as the dividing standard line , see Table 2 for the classification of the safety level of the glass curtain wall in use.

Table 2 The frequency range of the safety level of the curtain wall glass used in a certain building

Frequency range (Hz) 13～14.5 14.5～15.5 15.5～18 18～20 Security Level fall off There are hidden dangers Safe to use Reliable to use

On-site test detection:

The DLF-3 dual-channel filter integral amplifier produced by the Dongfang Vibration and Noise Technology Research Institute, the INV38V intelligent signal acquisition and processing analyzer and its supporting signal analysis software are used for vibration sampling. Select 10 pieces of representative glass for on-site test, each piece of glass is sampled three times, and the average frequency is taken as the measured frequency of the piece of glass. The sampling results are shown in Table 3.

Table 3 Sampling frequency of building curtain wall glass

evaluate:

Through on-site sampling and testing, the obtained natural frequency of each glass plate of the glass curtain wall falls within the range of safety levels shown in Table 2. Therefore, it is considered that the curtain wall is safe to use and can continue to be used without reinforcement and maintenance.

Claims (5)

1. A method for detecting loose glass curtain walls and predicting the risk of falling, using the following steps: 1) According to the parameters of the glass plate used in the glass curtain wall to be tested, determine the glass reference frequency range; 2) Determination of safety and reliability evaluation level: Carry out laboratory simulation tests on the same glass plate, measure the corresponding natural frequencies under different fixing conditions, and obtain the measurable frequency range ω _lower , ω _upper and loose frequency within the reference frequency range _ωloose ; the difference between the two extreme values _ωup and _ωdown of the measurable frequency range and the loosening frequency _ωloose is used as the safety interval and the dangerous interval for evaluation and classification; 3) On-site sampling test: use the corresponding excitation device and vibration pickup device to sample and detect the vibration signal of the glass curtain wall glass to obtain the measured frequency of the glass curtain wall; 4) Compare the measured frequency value measured on site in step 3) with the natural frequency classification in step 2), and obtain the safety and reliability level of the curtain wall glass in this service state according to the data comparison result. Among them, step 1) adopts the theoretical analysis method, corresponding to the four-sided simply supported fixing method of the glass, and calculates the lower limit value of the reference frequency by formula (1):

Corresponding to the fixing method of the four sides of the glass, the upper limit of the reference frequency is calculated by formula (2):

Among them: ω-natural frequency of glass, D-bending stiffness of tested sample,

- glass mass per unit area, a - glass length, b - glass width; where a and b are measured values,

According to the material of the sample to be tested from the manual or obtained from the original data of the curtain wall installation, the expression of the bending stiffness D is: D＝Eh ³ /12(1-υ ² ) (3) Among them: E-Young's modulus of glass material; h-glass thickness; υ-Poisson's ratio of glass material. 2. according to the described method of claim 1, it is characterized in that, step 2) described evaluation classification is four-point method: promptly loosening frequency ω _loosen is used as the standard dividing line of safety and reliability of glass curtain wall, and the lower limit value of measurable frequency range The _ωlower and _{ωloose intervals} are equally divided into two sections. From the lower limit value _ωlower to the _ωloose value, they correspond to the level of looseness and _shedding and the level of hidden dangers; Segment, from the ω _loose value _to the upper limit ω corresponds to the usage safety level and usage reliability level. 3. according to the described method of claim 1, it is characterized in that, step 2) described evaluation classification is four-point method: the _lower limit value ω of reference frequency and upper limit value ω are divided _into four sections equally, by numerical value from small to It is divided into four levels: loose and falling off, hidden danger, safe to use and reliable to use. 4. The method according to any one of claims 1 to 3, characterized in that the upper limit of the measurable frequency range of the measured value corresponds to the fixing method of the four sides of the glass, and the lower limit corresponds to the fixing method of the four sides of the glass simply supported. 5. The method according to any one of claims 1 to 3, characterized in that, the evaluation criteria of said step 4) is: when the actual measured frequency results are similar in the standard safe range, the curtain wall glass structure can be considered safe; When it falls in the dangerous zone, the structure is considered unsafe, and it is recommended to replace or take measures to strengthen its structure.

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