A method for determining a lightweight alarm threshold value for overloaded concrete beam bridges and its application

Abstract

The present invention discloses a method and use for determining a lightweight alarm threshold value for overloaded concrete beam bridges. First, a monitoring section that can represent the overloaded state and safety of the entire bridge is selected from the beam bridge control section; then, the lateral loading mode of a typical vehicle on the monitoring section is determined according to the equivalent principle of the most unfavorable beam or the most unfavorable measuring point effect of the monitoring section; finally, the maximum strain value of each measuring point on the monitoring section under each lateral loading mode is determined, and then the minimum value of the maximum strain value of each measuring point under different lateral loading modes is taken as the threshold value of the measuring point. The alarm threshold determined by the above method can construct a lightweight overload online monitoring alarm system, which can effectively monitor the passage of vehicles on the bridge that may cause the beam bridge to be overloaded. Regardless of the lateral loading mode in which the overweight vehicle on the bridge passes through the beam bridge, the measuring point can effectively sense the passage of the overweight vehicle and issue an alarm, providing a basis for the safe operation and supervision of the beam bridge.

Description

Technical Field

[0001] The invention belongs to the field of traffic management, in particular to an overload state monitoring and alarming technology for small and medium span concrete beam bridges. Background Art

[0002] Concrete beam bridges are one of the most common types of bridges, and their characteristic is that the main load is borne by concrete beams. For a long time, highway long beam bridges have been the focus of the construction of health structure monitoring systems. However, for a large number of medium and small span concrete beam bridges and large and extra-large bridges that are not included in the construction scope, especially medium and small span concrete beam bridges, due to the large design live load ratio (referring to the ratio of live load to dead load in the engineering structure), under the action of overweight vehicles, it is more likely to cause safety accidents such as structural damage or even collapse. Unlike the health monitoring system for long beam bridges, such medium and small spans and even large and extra-large continuous beam bridges with relatively simple structures that are not included in the construction implementation plan of the Ministry of Transport are not suitable for traditional health monitoring systems that cost hundreds of thousands or even millions of dollars. It is urgent to design a fast, economical and effective lightweight online monitoring system for structural safety status. How to monitor the safety status of the entire bridge with the least number of monitoring sections or measuring points is an important goal of lightweight monitoring system design.

[0003] Chinese patent application publication number CN106644326A discloses a bridge load limit rapid monitoring system based on dynamic deflection, which mainly includes a bridge dynamic deflection monitoring device, a data processing device, a vehicle information collection device and an overload information warning device. The detection system can be used to identify whether the overall equivalent weight of a truck passing through a bridge exceeds the actual safe load-bearing range of the bridge, thereby performing load limit monitoring on old bridges or bridges with damage in strong earthquake areas. However, the system requires multiple cameras to collect information related to vehicles traveling on the bridge (including license plate number, vehicle model, number of tires, driving position and driving lane), and the dynamic deflection detection device needs to set beam inclination sensors at multiple key positions (at least 5) of the bridge beam body. The installation procedure is complicated, which limits the application of this type of method in a large number of medium and small span bridges.

[0004] Chinese patent publication number CN109658711A discloses a bridge overload warning system, including a high-definition monitoring module, an advance warning module, a capture module, a dynamic weighing module, a bridge monitoring center, a data processing module and a model building module. The main technical solution of this warning system is to use the traffic big data collected by the dynamic weighing equipment to fit the random traffic load probability model generated, which truly reflects the actual load condition of the bridge deck, and can detect overloaded vehicles in time through overload prediction and real-time weighing comparison, so as to provide intelligent reminders and risk warnings. However, this technology requires multiple high-definition smart cameras to provide high-definition panoramic images of all vehicles on site in real time, and all vehicles in motion need to be dynamically weighed. The implementation process is relatively complicated and it is difficult to achieve lightweight monitoring.

[0005] The Chinese patent publication number CN115808324A discloses a lightweight safety management monitoring method and system for small and medium span bridges. Its main technical solution is to obtain the current environmental parameter information of the bridge to be tested, perform image processing on the target identification image of the identification target at the preset characteristic position, obtain the current bridge vibration information of the bridge to be tested at the preset characteristic position and the vehicle characteristics of the current target vehicle corresponding to the preset characteristic position, and then input the current bridge high-frequency three-dimensional displacement, current bridge temperature and humidity, current wind direction and wind speed, and vehicle characteristics into the pre-trained neural network evaluation and monitoring model to obtain the current bridge state of the bridge to be tested. This method considers the health influencing factors of small span bridges in detail, but has not yet determined the alarm threshold according to the bridge load limit theory, and cannot more intuitively evaluate whether the bridge structure has reached an overload state.

[0006] For large-span concrete beam bridges, independent health monitoring systems are generally built to monitor the safe operation status of beam bridges in real time. However, for a large number of medium and small span concrete beam bridges, no effective health monitoring system has been built, which has become a blind spot for the supervision of the safe operation status of the road network. For medium and small span in-service concrete beam bridges, compared with deflection monitoring, concrete surface strain is an extremely important alarm indicator. When calculating the strain threshold, it is still necessary to determine the mathematical relationship between the theoretical value and the measured value. Existing studies have mostly used different percentages of the theoretical model calculated value as the basis for the classification of the strain alarm threshold, which is far from meeting the accuracy requirements for concrete beam bridge overload state alarms.

[0007] In view of this, it is necessary to propose a method for determining the lightweight overload state alarm threshold to solve the above defects faced by small and medium span concrete beam bridges. Summary of the invention

[0008] In order to quickly, economically and effectively monitor the safety status of in-service small and medium-span concrete beam bridges, the present invention provides a method for determining a lightweight alarm threshold value for an overload state of a concrete beam bridge.

[0009] The invention also provides an application method of the threshold determined by this method.

[0010] To achieve the above object, the technical solution adopted by the present invention is:

[0011] A method for determining a lightweight alarm threshold value for an overload state of a concrete beam bridge, characterized in that it comprises the following steps:

[0012] Step 1: Determine the control section of the beam bridge and the corresponding load limit factor

[0013] According to the actual technical conditions of the beam bridge to be monitored, the most unfavorable section of each span is determined, which is called the control section. The number of control sections is represented by m. The load limit coefficient corresponding to each of the m control sections is calculated. ξ qi ( i =1,2,…,m);

[0014] Step 2: Determine the typical vehicle control load for full bridge overload condition W th

[0015] According to the load limit coefficient of each control section and the principle of effect equivalence, determine the typical vehicle weight limit corresponding to each control section. W thi ( i =1,2,…,m), the minimum value is taken as the typical vehicle control load in full bridge overload state W th ;

[0016] Step 3: Select the monitoring section of the beam bridge

[0017] A control section is selected from the m control sections as a monitoring section, and the overload state and safety performance of the selected monitoring section represent the overload state and safety of the whole bridge;

[0018] Step 4: Determine the overload alarm threshold for each measuring point on the monitoring section

[0019] 4.1: Determine the lateral loading pattern of typical vehicles on the monitoring section

[0020] The lateral loading pattern is determined by the typical number of vehicles j loaded laterally on the monitoring section and the correction value of the typical vehicle weight limit W Tj (j=1,2,…,n), where n=the number of lanes designed for the beam bridge to be monitored, thus obtaining the typical vehicle on the monitoring section n A horizontal loading mode;

[0021] The typical vehicle weight limit correction value means: j vehicles with a weight of WTj The effects of typical vehicles and their placement on the monitoring section k The weight is W th The effect produced by a typical vehicle is equivalent to that described k Refers to the number of lanes designed for beam bridge control ， That is, the number of lanes actually used in the design calculations for beam bridges;

[0022] 4.2: Determine the threshold value of each measuring point in the monitoring section

[0023] First, determine the maximum strain value of each measuring point on the monitoring section in each lateral loading mode. Then, for each measuring point, the minimum value of its maximum strain value under different lateral loading modes is taken as the threshold of the measuring point, that is, the overload alarm threshold of the measuring point on the monitoring section.

[0024] Furthermore, in step 2, the typical vehicle is determined according to the automobile load standard of the beam bridge design to be monitored.

[0025] Further: The principle followed in determining the monitoring section of the beam bridge in step three is: first select the control section that is easy to install the monitoring equipment, and then compare the typical vehicle weight limits corresponding to these control sections, and take the control section with the smallest typical vehicle weight limit as the monitoring section of the beam bridge.

[0026] Furthermore, when all control sections of the beam bridge are easy to install, the section whose typical vehicle weight limit is equal to the typical vehicle control load in the overload state of the entire bridge is selected as the monitoring section.

[0027] Further, the detailed method of step 4.1 is: taking the monitoring section determined in step 3 as the reference, taking the typical vehicle control load of the full bridge overload state determined in step 2 as the reference, W th Based on the equivalent principle of the most unfavorable beam or the most unfavorable measuring point effect of the monitoring section, the correction coefficient of the lateral multi-vehicle loading is calculated, and the lateral loading of one typical vehicle, two typical vehicles, etc. on the monitoring section is determined in turn. n Typical vehicle weight limit correction value corresponding to typical vehicles W Tj (j=1,2,…,n), typical vehicle weight limit correction value W Tj (j=1,2,…,n) and the number of lateral loads on typical vehicles constitute a lateral load pattern, and there are n lateral load patterns in total.

[0028] Furthermore, the measuring points described in step 4.1 are preferably selected to monitor the positions of the main beams on the cross section.

[0029] Furthermore, the detailed method of step 4.2 is: based on the n transverse loading modes determined in step 4.1, the most unfavorable transverse loading is performed on each measuring point on the monitoring section in turn, and the maximum strain value of each measuring point on the monitoring section is calculated. n The maximum strain value is the value of the strain at a certain measuring point. n The minimum strain value among the maximum strain values ​​is taken as the threshold value of the measuring point on the monitoring section.

[0030] The alarm threshold determined by the above method can be used to construct a lightweight overload online monitoring and alarm system to effectively monitor the passage of vehicles on the bridge that may cause the beam bridge to be overloaded. No matter what lateral loading mode the overweight vehicle on the bridge passes through the beam bridge, the measuring point can effectively sense the passage of the overweight vehicle and issue an alarm, providing a basis for the safe operation and supervision of the beam bridge.

[0031] The lightweight overload online monitoring and alarm system comprises a resistive strain sensor, a data collector, a controller, a signal transmission module and a core data processor installed on each main beam of the monitoring section. The resistive strain sensor is connected to the data collector by wire, the data collector is connected to the controller by wire, the controller is connected to the signal transmission module by Ethernet, and the signal transmission module is connected to the core data processor by wireless network; wherein:

[0032] The working method of the lightweight overload online monitoring and alarm system is as follows: when a vehicle passes through the beam bridge to be monitored, the resistive strain sensor installed at the measuring point monitors the micro-deformation of the measuring point when the vehicle passes by, the data collector collects the voltage signal of the resistive strain sensor in real time and summarizes it to the controller, transmits it to the core data processor through the signal transmission module, and analyzes and converts it into strain value in the core data processor; compares the real-time strain value of each measuring point with their respective thresholds, and makes corresponding alarms according to the size of the ratio.

[0033] Furthermore, the sensor and collector are connected by RVVP 4-core shielded wire, and the collector and controller are connected by RVVP 6-core shielded wire.

[0034] The positive effects of the present invention are:

[0035] 1. The present invention selects typical monitoring sections, calculates and sets multi-level alarm thresholds based on load limit theory, and achieves early detection and early prevention of overweight vehicles on the bridge to avoid structural damage. Applying the load limit theory of highway beam bridges, the limit of automobile load effect at a certain monitoring section or measuring point of the component can be determined. This limit is an important basis for calculating the strain or displacement threshold of the monitoring section or measuring point, providing technical support for overload state alarm and load limit management of concrete beam bridges with strain threshold as the control indicator, and is also an important prerequisite for realizing lightweight online monitoring and alarm of overload state of small and medium span beam bridges.

[0036] 2. The present invention can provide a complete online monitoring and alarm system for beam bridge structure safety for beam bridge maintenance units. The corresponding theoretical research results, monitoring and alarm systems, and software platforms can be extended to the overload status monitoring and alarm of common concrete beam bridges (including ordinary concrete and prestressed concrete beam bridges). By connecting with the smart highway platform, real-time monitoring and alarm of the safe operation status of road network beam bridges can be realized, which has important academic significance and engineering practical value for promoting the intelligent construction of highway beam bridge maintenance in my country. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0038] Figure 1 It is a schematic diagram of an embodiment of a lightweight overload online monitoring and alarm system constructed using the threshold value of the present invention.

[0039] Figure 2 It is an alarm flow chart of an embodiment of a lightweight overload online monitoring alarm system constructed using the threshold value of the present invention.

[0040] Figure 3 This is a typical vehicle schematic diagram selected for application examples, showing the axle weight and wheelbase. DETAILED DESCRIPTION

[0041] The technical solutions in the embodiments of the present invention are described clearly and completely below in conjunction with the accompanying drawings.

[0042] In order to facilitate understanding of the technical solution of the alarm threshold determination method of the present invention, the following is a case where the number of designed lanes of the beam bridge is n=4 and the number of designed lanes of the control is n=4. k =2 、 This is explained by taking an existing beam bridge with a span of 5 as an example.

[0043] Step 1: Determine the control section of the beam bridge and the corresponding load limit factor

[0044] According to the actual technical conditions of the beam bridge, in accordance with the "Highway Reinforced Concrete and Prestressed Concrete Bridge and Culvert Design Code" (JTG 3362-2018) and the "Highway Bridge Bearing Capacity Test and Assessment Procedure" (JTG / T J21-2011), the most unfavorable section of each span of the beam bridge, that is, the control section, is determined. There are five control sections in the five spans, which are called the first control section, the second control section, the third control section, the fourth control section and the fifth control section; then the load limit coefficients corresponding to the five control sections are calculated according to the "Highway Bridge Load Limit Theory and Application Guide" ξ q1 , ξ q2 , ξ q2 , ξ q4 , ξ q5 ;

[0045] Step 2: Determine the typical vehicle control load for full bridge overload condition W th

[0046] First, according to the automobile load standard of the beam bridge design, the typical vehicle model is determined. Then, according to the load limit coefficients of the five control sections and the principle of effect equivalence, the typical vehicle weight limit corresponding to the first to fifth control sections is determined. W thi ( i =1,2,…,5), the minimum value is taken as the typical vehicle control load in full bridge overload state W th , assuming that the typical vehicle weight limit corresponding to the fourth control section is W th4 Minimum, then W th = W th4 ;

[0047] Step 3: Select the monitoring section of the beam bridge

[0048] Compare the difficulty of installing monitoring equipment on the five control sections. If it is found that the third and second control sections are easy to install, and the third control section corresponds to the typical vehicle weight limit W th3 Less than the typical vehicle weight limit corresponding to the second control section W th2 , then the third control section is selected as the monitoring section of the beam bridge, and its overload status and safety performance represent the overload status and safety of the whole bridge;

[0049] Step 4: Determine the overload alarm threshold for each measuring point on the monitoring section

[0050] 4.1: Determine the lateral loading pattern of typical vehicles on the monitoring section

[0051] Based on the monitoring section determined in step 3, i.e. the third control section, and the typical vehicle control load of the full bridge overload state determined in step 2, W th Based on the equivalent principle of the most unfavorable beam or the most unfavorable measuring point effect of the monitoring section, the correction coefficient of the lateral multi-vehicle loading is calculated, and the corresponding correction values ​​of the typical vehicle weight limit when one typical vehicle, two typical vehicles, ... four typical vehicles are horizontally loaded on the monitoring section, that is, the third control section, are determined in turn. W Tj (j=1,2,…,4), typical vehicle weight limit correction value W Tj (j=1,2,…,4) and the number of lateral loads of typical vehicles constitute the lateral load pattern of typical vehicles on the monitoring section. There are four lateral load patterns in total;

[0052] 4.2: Determine the threshold value of each measuring point in the monitoring section

[0053] Based on the four transverse loading modes determined in step 4.1, the most unfavorable transverse loading is performed on each measuring point on the monitoring section, that is, the third control section, and the maximum strain value of each measuring point on the monitoring section is calculated. Four maximum strain values ​​can be obtained for each measuring point on the monitoring section. For example, for the l The corresponding maximum strain value is ε lj ( j =1, 2, 3, 4), for the l The minimum value of the four maximum strain values ​​of the measuring point is the threshold value of the measuring point, that is, the l Overload alarm threshold of measuring point No.

[0054] According to the following Figure 1 The lightweight overload online monitoring and alarm system constructed by the present invention is described. Figure 1It can be seen that the overall system includes a resistive strain sensor, a data collector, a controller, a signal transmission module and a core data processor; the connection relationship between the above components is: the resistive strain sensor and the data collector are connected by RVVP 4-core shielded wires, which have strong anti-electromagnetic interference ability, good conductivity, and are not easy to heat up, and can effectively reduce the impact of external environmental noise on sensor data acquisition; the data collector and the controller are connected by RVVP 6-core shielded wires; the controller and the signal transmission module are connected by Ethernet; the signal transmission module and the core data processor are connected by a wireless network. The signal transmission module of the present invention can use an IR912 industrial-grade LTE router, which has complete and intelligent software functions and a complete industrial hardware platform, providing reliable, high-speed and secure network connections for remote devices.

[0055] The above-mentioned data collector is a strain collector, which together with the controller constitutes a data acquisition system. The present invention adopts the DH5971 distributed data acquisition system. Each controller has 2 communication outputs, each of which supports a maximum of 8 collectors in series, and each acquisition module supports a maximum of 4 channels of data acquisition, that is, each controller can monitor 64 measuring points at the same time.

[0056] Combine the following Figure 2 and one The alarm embodiment illustrates how the lightweight overload online monitoring alarm system of the present invention alarms. In the embodiment, in order to save costs and improve the accuracy of the alarm, a first-level alarm and a second-level alarm are set. The first-level alarm mainly supervises and counts the operating status of the beam bridge to be monitored. The threshold is set to 85% of the maximum theoretical data of each measuring point under the safe operating state. When a first-level alarm occurs, it is only alarmed in the system software, and no text messages or emails are sent in real time. Instead, statistics are performed once a day and the statistical results are fed back. The first-level alarm can prompt the relevant users and persons in charge of the beam bridge to be monitored, and increase the degree of attention to the recent operation of the beam bridge. The second-level alarm plays the role of real-time alarm. The threshold is set to the maximum theoretical data of each measuring point under the safe operating state. Once the second-level alarm threshold is exceeded, the system automatically alarms and sends alarm information to the relevant users, including the alarm measuring point number, alarm time, and data value exceeding the threshold.

[0057] See also Figure 2After the system starts monitoring, it automatically receives the real-time monitoring data transmitted by each measuring point, compares the strain value of each measuring point processed by the core data processor with the respective alarm threshold, and determines whether it exceeds the alarm threshold. If the strain value of a certain point does not exceed the first-level alarm threshold of the measuring point, the monitoring data of the measuring point is stored in the general database and continues to be monitored; if a certain measuring point exceeds the first-level alarm threshold of the measuring point but does not exceed the second-level alarm threshold, the monitoring data of the measuring point is stored in the early warning database and an alarm is issued in the system software. If the second-level alarm threshold of the measuring point has been exceeded, the monitoring data of the measuring point is stored in the early warning database and an alarm message is issued. Among them, the general database stores all measuring point numbers and their strain values, and the early warning database stores the measuring point numbers and strain values ​​that exceed the first and second-level alarm thresholds.

[0058] The following takes the approach bridge of the Yuping-Yihe Bridge in Linyi City and across the Yihe River as an example to further illustrate the determination process of the threshold value of the present invention. The bridge is a 5-span assembled prestressed concrete box-shaped continuous beam bridge with a total of 8 main beams and a designed number of lanes n=6. The specific steps are as follows:

[0059] Step 1: Determine the control section of the beam bridge and the load limit coefficient of each control section according to the actual technical conditions of the beam bridge

[0060] First, through the investigation of the actual technical status of the approach bridge of Yuping-Yihe Bridge, the control section of the approach bridge of Yuping-Yihe Bridge was calculated according to the "Design Code for Highway Reinforced Concrete and Prestressed Concrete Bridges and Culverts" (JTG 3362-2018) and the "Highway Bridge Bearing Capacity Test and Assessment Code" (JTG / T J21-2011). After calculation, the No. 5 beam is the most unfavorable beam, and its control section is: the mid-span section of the first span (called the first control section), the mid-span section of the second span (called the second control section), and the mid-span section of the third span (called the third control section). Since the bridge is a prestressed concrete box-shaped continuous beam bridge with 5 spans arranged symmetrically, only spans 1 to 3 are selected for calculation for the convenience of calculation, that is, m=3.

[0061] Then, based on the load limit theory of beam bridges and the actual engineering conditions of the approach bridge of the Yuping-Yihe Bridge, a structural function function that comprehensively considers multiple factors is constructed to calculate the load limit coefficients corresponding to each control section. ξ q1 =1.424, ξ q2 =1.418, ξ q3 =1.443.

[0062] Step 2: Determine the typical vehicle control load of the full bridge overload state based on the load limit analysis of the beam bridge W th

[0063] Considering that the Yuping-Yihe Bridge is designed according to the highway-I lane load standard, a 55t five-axle heavy-duty vehicle will be used as a standard typical vehicle load model for calculation in the load limit analysis of the bridge. The wheel weight and wheelbase of the 55t five-axle heavy-duty vehicle are shown in Figure 3 , Figure 3 The wheelbase unit is meter.

[0064] According to the load limit coefficients of the three control sections and the principle of effect equivalence, the typical vehicle weight limit corresponding to the first to third control sections is calculated and determined by formula (1): W th1 =86.28t, W th2 =82.81t, W th3 =83.06t, the minimum value 82.81t is taken as the typical vehicle control load in the full bridge overload state W th ;

[0065] (1)

[0066] Where W is the vehicle weight of the standard vehicle load model, W=55t; R i is the effect coefficient of each control section. According to the effect equivalence principle, the effect coefficients of each section are R1=1.102, R2=1.062, and R3=1.047 respectively.

[0067] Step 3: Selection of monitoring section for beam bridge

[0068] First, a control section that is easy to install monitoring equipment is selected. After an in-depth investigation and evaluation of the site, the clear height of the first control section is too low, which poses an unfavorable factor to the protection work of the monitoring equipment. The second control section is below the city main road. Due to safety and traffic flow considerations, monitoring equipment cannot be installed here. Therefore, the third control section is finally selected as the representative of the overload status and safety performance of the entire bridge.

[0069] Step 4: Determine the overload alarm threshold for each measuring point on the monitoring section

[0070] 4.1: Determine the lateral loading pattern of typical vehicles on the monitoring section

[0071] Based on the monitoring section determined in step 3, i.e. the third control section, and the typical vehicle control load of the full bridge overload state determined in step 2, W th =82.81t, and calculate the lateral multi-car load correction factor according to the equivalent principle of the most unfavorable beam or the most unfavorable measuring point effect of the monitored section. m Tj, and determine the corresponding typical vehicle weight limit correction value when one typical vehicle, two typical vehicles, ... six typical vehicles are horizontally loaded on the monitoring section, that is, the third control section. W Tj (j=1,2,…,6), typical vehicle weight limit correction value W Tj (j=1,2,…,6) and the number of lateral loads on typical vehicles constitute a lateral load pattern. There are six lateral load patterns in total.

[0072] Among them, the typical vehicle weight limit correction value W Tj (j=1,2,…,6) Calculate according to formula (2), the correction factor of lateral multi-vehicle load m Tj and typical vehicle weight limit correction values W Tj The calculation results are shown in Table 1;

[0073] (2).

[0074] Table 1

[0075]

[0076] 4.2: Determine the threshold value of each measuring point in the monitoring section

[0077] The bridge has a total of 8 box girders, arranged symmetrically. In order to simplify the calculation, only beams 5 to 8 are selected, and the measuring points are set at the bottom of the web of the box girders of beams 5 to 8, with a total of 4 measuring points.

[0078] Based on the six typical vehicle lateral loading modes determined in step 4.1, the most unfavorable lateral loading is carried out on the four measuring points on the monitoring section in turn, and the maximum strain values ​​of the four measuring points on the monitoring section are calculated using finite element software. Six maximum strain values ​​can be obtained at each measuring point on the monitoring section. The calculation results are shown in Table 2.

[0079] Table 2

[0080]

[0081] It can be seen from Table 2 that the minimum value of the maximum strain value of the first measuring point is 99.8με, the minimum value of the maximum strain value of the second measuring point is 77.9με, the minimum value of the maximum strain value of the third measuring point is 69.0με, and the minimum value of the maximum strain value of the fourth measuring point is 63.4με. Therefore, the minimum value of the maximum strain value of each measuring point is the threshold of the measuring point, that is, the overload alarm threshold of each measuring point on the monitoring section.

[0082] The above is only an embodiment of the present invention and is not intended to limit the technical solution of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for determining a lightweight alarm threshold value for overloaded concrete beam bridges, characterized in that: The following steps are involved: Step 1: Determine the control section of the beam bridge and the corresponding load limit factor: According to the actual technical conditions of the beam bridge to be monitored, the most unfavorable section of each span is determined, which is called the control section. The number of control sections is represented by m. The load limit coefficient corresponding to each of the m control sections is calculated. ξ qi ( i =1,2,…,m); Step 2: Determine the typical vehicle control load for full bridge overload condition W th : According to the load limit coefficient of each control section and the principle of effect equivalence, determine the typical vehicle weight limit corresponding to each control section. W thi ( i =1,2,…,m), the minimum value is taken as the typical vehicle control load in full bridge overload state W th ; Step 3: Select the monitoring section of the beam bridge: Select one control section from the m control sections as the monitoring section. The overload status and safety performance of the selected monitoring section represent the overload status and safety of the entire bridge. The principle followed in determining the monitoring section of the beam bridge is: first select a control section that is easy to install monitoring equipment, then compare the typical vehicle weight limits corresponding to these control sections, and select the control section with the smallest typical vehicle weight limit as the monitoring section of the beam bridge; Step 4: Determine the overload alarm threshold for each measuring point on the monitoring section: 4.1: Determine the lateral loading pattern of typical vehicles on the monitoring section: The lateral loading pattern is determined by the typical number of vehicles j loaded laterally on the monitoring section and the correction value of the typical vehicle weight limit W Tj (j=1,2,…,n), where n=the number of lanes designed for the beam bridge to be monitored, thus obtaining the typical vehicle on the monitoring section n A horizontal loading mode; The detailed method is: take the monitoring section determined in step 3 as the benchmark, and the typical vehicle control load of the full bridge overload state determined in step 2 as the benchmark. W th Based on the equivalent principle of the most unfavorable beam or the most unfavorable measuring point effect of the monitoring section, the correction coefficient of the lateral multi-vehicle loading is calculated, and the lateral loading of one typical vehicle, two typical vehicles, etc. on the monitoring section is determined in turn. n Typical vehicle weight limit correction value corresponding to typical vehicles W Tj (j=1,2,…,n), typical vehicle weight limit correction value W Tj (j=1,2,…,n) and the number of lateral loads on typical vehicles constitute a lateral load pattern, and there are n lateral load patterns in total; The typical vehicle weight limit correction value means: j vehicles with a weight of W Tj The effects of typical vehicles and their placement on the monitoring section k The weight is W th The effect produced by a typical vehicle is equivalent to that described k It refers to the number of lanes designed for beam bridge control; 4.2: Determine the threshold value of each measuring point in the monitoring section: First, determine the maximum strain value of each measuring point on the monitoring section under each transverse loading mode, and then take the minimum value of the maximum strain value of each measuring point under different transverse loading modes as the threshold of the measuring point, that is, the overload alarm threshold of the measuring point on the monitoring section; The detailed method is as follows: Based on the n transverse loading modes determined in step 4.1, the most unfavorable transverse loading is performed on each measuring point on the monitoring section in turn, and the maximum strain value of each measuring point on the monitoring section is calculated. n The maximum strain value is the value of the strain at a certain measuring point. n The minimum strain value among the maximum strain values ​​is taken as the threshold value of the measuring point on the monitoring section; the measuring point is selected from the position of each main beam on the monitoring section.

2. The method for determining the lightweight alarm threshold of overload state of a concrete beam bridge according to claim 1, characterized in that: In step 2, the typical vehicle is determined according to the automobile load standard of the beam bridge to be monitored.

3. The method for determining the lightweight alarm threshold value of overload state of a concrete beam bridge according to claim 1, characterized in that: When all control sections of a beam bridge are easy to install, the section with a typical vehicle weight limit equal to the typical vehicle control load of the full bridge overload state is selected as the monitoring section.

4. A method for applying the threshold value determined by the method for determining the lightweight alarm threshold value of overload state of a concrete beam bridge according to any one of claims 1 to 3, characterized in that: The threshold value is used to construct a lightweight overload online monitoring and alarm system, which includes a resistive strain sensor installed on each main beam of the monitoring section, a data collector, a controller, a signal transmission module and a core data processor. The resistive strain sensor is connected to the data collector by wire, the data collector is connected to the controller by wire, the controller is connected to the signal transmission module by Ethernet, and the signal transmission module is connected to the core data processor by wireless network; wherein: The working method of the lightweight overload online monitoring and alarm system is as follows: when a vehicle passes through the beam bridge to be monitored, the resistive strain sensor installed at the measuring point detects the micro-deformation of the measuring point when the vehicle passes by, the data collector collects the voltage signal of the resistive strain sensor in real time and summarizes it to the controller, transmits it to the core data processor through the signal transmission module, and analyzes and converts it into strain value in the core data processor; compares the real-time strain value of each measuring point with their respective thresholds, and makes corresponding alarms according to the size of the ratio.

5. The threshold application method determined by the method for determining the lightweight alarm threshold of overload state of concrete beam bridge according to claim 4 is characterized in that: The resistive strain sensor is connected to the data collector by using a RVVP 4-core shielded wire, and the data collector is connected to the controller by using a RVVP 6-core shielded wire.

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