An automatic monitoring method for deflection of an arc-shaped truss structure based on deformation measurement of a rod between nodes

Abstract

The application discloses a kind of based on the deflection automatic monitoring method of arc truss structure of deformation measurement between nodes. The deflection automatic detection method includes the following steps: (1) optical fiber grating sensor is arranged between adjacent nodes of a truss;(2) the distance change value between each node is obtained according to optical fiber grating sensor, and the initial value is calculated to obtain the actual distance between each node in use process;(3) the measured distance between each node is brought into the deduced deflection calculation formula by software, and the real-time deflection value is obtained;(4) the deflection value calculated is compared with specification limit, when deflection value exceeds specification limit, the device issues an alarm.The application can realize whole process, uninterrupted monitoring of truss structure by only once installation, eliminates the hysteresis problem of periodic inspection, and the whole deformation of truss can be measured by the method, and the deflection of each truss of truss structure is monitored.

Description

Technical Field

[0001] This invention provides an automatic monitoring method for the deflection of an arc truss structure based on the measurement of deformation of members between nodes, belonging to the field of building engineering automation monitoring technology. Background Technology

[0002] Arched truss structures are a type of steel space frame structure, primarily used in large public buildings. During use, due to external forces or inherent defects, truss structures undergo deformation. To ensure the performance and safety of these structures, real-time monitoring is necessary, with deflection detection being a crucial aspect of building operation and safety monitoring. Currently, monitoring primarily relies on manual observation or deflection measurements using tools such as total stations and steel rulers. However, these methods often produce results with time lags, failing to detect problems promptly. Therefore, to enable real-time monitoring and feedback of truss structure deformation, it is essential to research a fully automated, all-weather, and uninterrupted method for monitoring truss structure deflection. Summary of the Invention

[0003] To address the technical challenge of existing monitoring technologies' inability to monitor and report the deformation of truss structures in real time, this invention proposes an automatic deflection monitoring method for arc-shaped truss structures based on the measurement of member deformation between nodes. An arc-shaped truss structure consists of multiple members and nodes, divided into upper and lower chords. Deflection measurement specifically refers to the deformation measurement of the lower chords. First, using calculus concepts, the structure composed of all lower chords of a steel truss is approximated as an arc, allowing the initial relationship between the length of each lower chord and the arc height at its midpoint to be calculated. Then, based on the deployed sensors, the axial deformation of a single or multiple members of the truss is obtained. Furthermore, the change in arc height, i.e., the deflection value of the intermediate node of a steel truss, is obtained through the deformation of the axial dimensions of the lower chords. The obtained deflection value is compared with the design value and the specification limits to assess the safety of the steel truss structure.

[0004] The technical solution of the present invention is as follows:

[0005] An automatic deflection monitoring method for arc-shaped truss structures based on deformation measurement of members between nodes is proposed. This method can be used to monitor deflection changes of arc-shaped truss structures during use. The specific steps include:

[0006] (1) Fiber grating deformation sensors are sequentially installed between each node of the lower chord of an arc truss structure whose deflection change needs to be measured. The deformation measured by the sensors is the axial deformation of the metal rod connecting the two nodes. The deformation of the rod between the nodes is obtained by the fiber grating sensors, and the data is recorded by the acquisition device.

[0007] The fiber optic grating sensor needs to be pre-stretched during deployment, and its two ends are fixedly installed on adjacent nodes. The fixing points are firm and reliable, and no deformation occurs during long-term monitoring.

[0008] Furthermore, the fiber optic grating sensor of the present invention is fixed at both ends to ball nodes or supports at the nodes, and the initial distance between the two nodes is determined according to on-site measurements.

[0009] (2) The expression for the arc height is obtained by calculating the distance between each node. The derivation process of the expression for the arc height is as follows:

[0010] The support nodes at one end of the truss are numbered a1, a2 is the spherical node adjacent to a1, a3 is adjacent to a2, and so on. The support nodes at the other end of the truss are numbered a... m The truss is fixed at both ends and has m-1 nodes with a spacing of d between adjacent nodes. i According to the calculus theorem, the truss can be approximated as a circular arc, and its arc length l can be expressed as:

[0011]

[0012] Support a1 and support a m The straight-line distance between them is 2a, which means the chord length of the arc is 2a. Therefore, the truss arc length l and the support spacing 2a form an arc with a radius of R, an arc height of h, and a radian length of α.

[0013] The radius R of the arc has the following relationship with the arc height h and the support spacing 2a:

[0014] R2-a 2 =(Rh) 2

[0015] Right now

[0016]

[0017] According to the basic knowledge of circular arcs:

[0018] l=α·R (2)

[0019]

[0020] Substituting formula (2) into formula (3) yields...

[0021]

[0022] The result can be obtained from the Taylor series expansion formula of trigonometric functions.

[0023]

[0024] Simplified, we can obtain

[0025]

[0026] Substituting formula (6) into formula (2) yields the expression for R:

[0027]

[0028] Substituting formula (7) into formula (1) yields the expression for the arc height h:

[0029]

[0030] in

[0031]

[0032] The above formula Substituting into formula (8), we obtain the expression for the arc height h:

[0033]

[0034] Formula 9 is the expression for the initial arc height at the midpoint of the lower chord of the truss, where 'a' represents the support nodes a1 and a2. m Half the straight-line distance between them is a fixed value, therefore the value of h is only related to d. i Related, when d i When changes occur, i.e., when one or more members of the truss structure deform, the distance changes between each node are acquired using deployed fiber optic grating sensors and compared with the initial values ​​to obtain the actual distance d between the nodes of the truss during use. i The corresponding arc height h becomes h′, and the monitored truss deflection value δ is expressed as:

[0035] δ=hh′ (10)

[0036] (3) The measured distance between each node is input into the derived deflection calculation formula through software, and the deflection value δ at the midpoint of the truss is calculated in real time and compared with the standard limit. When the limit is exceeded, the machine will automatically issue an alarm.

[0037] The fiber optic grating sensor is mainly used to measure the change in axial displacement caused by the deformation of metal rods, that is, the change in the straight distance between two nodes. Since deformation sensors are evenly distributed between each node, the deformation of each rod can be obtained while monitoring the deflection value at the midpoint.

[0038] For truss deformation measurement, a truss between two supports is taken as a monitoring unit. Multiple lines can be laid out simultaneously according to the actual site conditions to monitor the deflection of each truss in the truss structure.

[0039] With just one installation, the sensor can continuously collect the deformation of the rod around the clock, and calculate the deflection value δ at the midpoint in real time through software. The value is then compared with the standard limit, and the machine will automatically issue an alarm when the limit is exceeded.

[0040] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0041] (1) The entire process of continuous monitoring of the truss structure can be achieved with just one installation. The deflection value δ at the midpoint is calculated in real time by the software and compared with the standard limit. When the limit is exceeded, the machine will automatically issue an alarm, eliminating the problem of lag in regular inspections.

[0042] (2) This method can simultaneously measure the deformation of any member. Based on the derived deflection calculation method, the obtained deformation values ​​of a single member or multiple members are substituted into the formula to calculate the deflection value.

[0043] (3) This method can be used to measure the overall deformation of the truss. A truss between two supports is a monitoring unit. Multiple lines can be laid out according to the actual site conditions to monitor the deflection of each truss in the truss structure. Attached Figure Description

[0044] Figure 1 This is a flowchart illustrating the automatic deflection monitoring method for arc-shaped truss structures based on the deformation measurement of members between nodes, as described in this invention.

[0045] Figure 2 This is a schematic diagram of the fiber optic grating layout between the pole nodes described in this invention.

[0046] Figure 3 This is a schematic diagram illustrating the derivation process of the arc truss structure deflection calculation method based on the deformation measurement of members between nodes as described in this invention. Specific implementation methods

[0047] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0048] like Figure 1 The diagram shown is a flowchart illustrating an automatic deflection monitoring method for an arc-shaped truss structure based on deformation measurement of members between nodes, according to an embodiment of the present invention. The method includes the following steps:

[0049] (1) Fiber grating sensors are sequentially installed between adjacent nodes of a truss. The two ends of the sensors are fixed to the ball nodes or supports at the nodes. The initial distance between the two nodes is determined based on on-site measurements.

[0050] It should be noted that the fiber optic grating sensor involved in this embodiment needs to be pre-stretched during deployment, and its fixing points are firm and reliable, and will not deform during long-term monitoring.

[0051] (2) The expression for the arc height is obtained by calculating the distance between each node. The derivation process of the expression for the arc height is as follows:

[0052] The support nodes at one end of the truss are numbered a1, a2 is the spherical node adjacent to a1, a3 is adjacent to a2, and so on. The support nodes at the other end of the truss are numbered a... m The truss is fixed at both ends and has m-1 nodes with a spacing of d between adjacent nodes. i According to the calculus theorem, the truss can be approximated as a circular arc, and its arc length l can be expressed as:

[0053]

[0054] Support a1 and support a m The straight-line distance between them is 2a, which means the chord length of the arc is 2a. Therefore, the truss arc length l and the support spacing 2a form an arc with a radius of R, an arc height of h, and a radian length of α.

[0055] The radius R of the arc has the following relationship with the arc height h and the support spacing 2a:

[0056] R2-a 2 =(Rh) 2

[0057] Right now

[0058]

[0059] According to the basic knowledge of circular arcs:

[0060] l=a·R (2)

[0061]

[0062] Substituting formula (2) into formula (3) yields...

[0063]

[0064] The result can be obtained from the Taylor series expansion formula of trigonometric functions.

[0065]

[0066] Simplified, we can obtain

[0067]

[0068] Substituting formula (6) into formula (2) yields the expression for R:

[0069]

[0070] Substituting formula (7) into formula (1) yields the expression for the arc height h:

[0071]

[0072] in

[0073]

[0074] The above formula Substituting into formula (8), we obtain the expression for the arc height h:

[0075]

[0076] Formula 9 is the expression for the initial arc height at the midpoint of the lower chord of the truss, where 'a' represents the support nodes a1 and a2. m Half the straight-line distance between them is a fixed value, therefore the value of h is only related to d. i Related, when d i When changes occur, i.e., when one or more members of the truss structure deform, the distance changes between each node are acquired using deployed fiber optic grating sensors and compared with the initial values ​​to obtain the actual distance d between the nodes of the truss during use. i The corresponding arc height h becomes h′, and the monitored truss deflection value δ is expressed as:

[0077] δ=hh′ (10)

[0078] (3) The measured distance between each node is input into the derived deflection calculation formula by using software to calculate the real-time deflection value;

[0079] (4) Compare the calculated deflection value with the standard limit. When the deflection value exceeds the standard limit, the equipment will issue an alarm. Example

[0080] An automatic deflection monitoring method for arc-shaped truss structures based on deformation measurement of members between nodes is illustrated with an engineering example. The specific testing steps are as follows:

[0081] a. The roof of a museum project adopts a truss structure, consisting of 7 main trusses. The main trusses are large-span hexagonal space tube truss structures. Monitoring is being conducted on the lower chord of the fourth truss. The members are of two lengths: 4 meters and 3 meters. Supports a1 and a... m Fixed to the top of the concrete column, and at the same height. Between nodes a1-a2, a m-1 -am The length of the members between nodes is 3 meters, and the length of the members between all other nodes is 4 meters, for a total of 56 members, with a value of m of 57; a1 and a m The distance between them is 220 meters, meaning 'a' is 110 meters. The measured arc height using a total station is 12.76 meters.

[0082] b. Install fiber optic grating sensors between adjacent nodes of a truss. The two ends of the sensors are fixed to the ball nodes or supports at the nodes, and the sensor values ​​are transmitted back to the computer in real time.

[0083] c. The arc height h calculated using this invention is 12.84 meters, with an error of 0.63% compared to the total station measurement, indicating high accuracy.

[0084] d. Because the truss structure was constructed in summer, the high temperatures caused deformation of the steel structure. 12 -a 13 Sensors between nodes indicate that the rod has deformed, with a deformation value of 0.005 meters. 27 -a 28 The sensors between the nodes showed that the rods had deformed, with a deformation value of 0.007 meters. The arc height h changed to 12.81 meters, and the deflection value δ was hh′=0.03 ​​meters.

[0085] e. On-site verification, a 12 -a 13 Between nodes, a 27 -a 28 The members between the nodes deformed, and the deformation value was the same as the value measured by the fiber optic grating sensor.

[0086] f. The arc height was measured to be 12.80 meters on site using a total station. The error between the calculated and measured values ​​was 0.08%, indicating high accuracy.

Claims

1. An automatic monitoring method for the deflection of an arc-shaped truss structure based on the measurement of deformation of members between nodes, characterized in that, The specific steps include: (1) Fiber grating deformation sensors are sequentially installed between each node of the lower chord of an arc truss structure whose deflection change needs to be measured. The deformation measured by the sensors is the axial deformation of the metal rod connecting the two nodes. The deformation of the rod between the nodes is obtained by the fiber grating sensors, and the data is recorded by the acquisition device. (2) The expression for the arc height is obtained by calculating the distance between each node. The derivation process of the expression for the arc height is as follows: The node number of one end support of the truss is a1, the ball nodes adjacent to a1 are a2, a3 is adjacent to a2, and the other end support of the truss is sequentially numbered as a m The truss is fixed at both ends, and the truss has m-1 node intervals, and the initial straight line distance between adjacent nodes is d i According to the calculus theorem, the truss is approximately expressed in a circular arc shape, and the arc length l can be expressed as: Support a1 and support a m The straight line distance between support a1 and support a is 2a, that is, the chord length of the circular arc is 2a, so that the truss arc length l and the support spacing 2a form a circular arc, and the corresponding circular arc radius is R, the arc height is h, and the arc length l corresponds to the radian α. The radius R of the arc has the following relationship with the arc height h and the support spacing 2a: R 2 -a 2 = (R - h) 2 Right now According to the basic knowledge of circular arcs: l＝α·R (2) Substituting formula (2) into formula (3) yields... The result can be obtained from the Taylor series expansion formula of trigonometric functions. Simplified, we can obtain Substituting formula (6) into formula (2) yields the expression for R: Substituting formula (7) into formula (1) yields the expression for the arc height h: in The above formula Substituting into formula (8), we obtain the expression for the arc height h: Formula (9) is the expression for the initial arc height of the midpoint of the lower chord of the truss, where a is the support node a1 and a2. m Half the straight-line distance between them is a fixed value, therefore the value of h is only related to d. i Related, when d i When changes occur, i.e., when one or more members of the truss structure deform, the distance changes between each node are acquired using deployed fiber optic grating sensors and compared with the initial values ​​to obtain the actual distance d between the nodes of the truss during use. i The corresponding arc height h becomes h′, and the monitored truss deflection value δ is expressed as: δ=hh′ (10) (3) The measured distance between each node is substituted into the derived deflection calculation formula through software to calculate the deflection value δ at the midpoint of the truss in real time and compare it with the standard limit. When the limit is exceeded, an alarm is issued.

2. The automatic monitoring method for deflection of an arc-shaped truss structure based on deformation measurement of members between nodes, as described in claim 1, is characterized in that... The fiber optic grating sensor needs to be pre-stretched during deployment, and its two ends are fixedly installed on adjacent nodes, with the fixing points being firm and reliable.

3. The automatic monitoring method for deflection of an arc-shaped truss structure based on deformation measurement of members between nodes, as described in claim 2, is characterized in that... The fiber optic grating sensor is fixed at both ends to the ball nodes or supports at the nodes, and the initial distance between the two nodes is determined based on on-site measurements.

4. The automatic monitoring method for deflection of an arc-shaped truss structure based on the measurement of deformation of members between nodes, as described in any one of claims 1 to 3, is characterized in that... For truss deformation measurement, a truss between two supports is taken as a monitoring unit. Multiple lines can be laid out simultaneously according to the actual site conditions to monitor the deflection of each truss in the truss structure.

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