What is the detection technology of highway bridges? How is it defined? Please read the article by the editor of Zhongda Consulting.
1. Overview
1.1 Definition of bridge structure inspection
Bridge structure inspection is mainly an investigation of the technical condition of the bridge, that is, the detection of bridge defects and damage nature, location, severity and development trends, identify the main causes of defects and damage, analyze and comment on their impact on the quality and load-bearing capacity of the bridge, and provide reliable technical data and basis for bridge maintenance and reinforcement design. The work that the bridge inspection room must carry out before the bridge is maintained, repaired and reinforced is a reliable guarantee for determining whether the maintenance and reinforcement plan is feasible and correct. It is also an indispensable and important step in the bridge assessment, maintenance, repair and reinforcement work. components.
1.2 Structural types of bridges in Guizhou
Guizhou has a typical karst landform, and the province’s landforms can be broadly divided into three types: plateau mountains, hills and basins. The rivers in Guizhou are located in the intersection zone of the upper reaches of the Yangtze River and the Pearl River. The province's water system flows along the terrain from the west and central to the north and southeast. Therefore, there are relatively many types of bridge structures in mountainous areas and the structures are relatively complex. There are mainly beam bridges (mainly with T-beams and continuous box girders as the development trend), slab bridges, cable-stayed bridges, reinforced concrete arch bridges, suspension bridges and stone arch bridges.
2. Methods of bridge engineering inspection
With the increasing traffic density and vehicle load in our country, and the increasing transportation volume, bridges in long-term use will inevitably suffer from overloading and other factors If damage occurs, if it is not repaired and some reinforcement measures are not taken, the durability and load-bearing capacity of the bridge will be reduced, and serious traffic accidents may occur. This article will also further discuss the common points and methods of bridge engineering inspection.
2.1 Bridge appearance inspection methods and key points
The appearance inspection includes the measurement of the overall and local structural geometric dimensions of the bridge, the inspection and measurement of structural diseases, etc. Different bridge types Each has its own emphasis on inspection. Generally speaking, the bridge can be divided into three parts as a whole:
(1) Superstructure, which mainly refers to the main beam in beam bridges;
(2) Substructure, generally Including foundation and cap, arch ring vault cracks, pier displacement, piles and abutments, etc.;
(3) Ancillary structures should generally focus on checking the bridge deck pavement, expansion joints, railings, etc., and other There are also inspection points such as diagonal cracks at the ends of the beam bridge and cracks and deflections at the mid-span. For the type of reinforced concrete bridge, it is mainly to detect the steel bars (protective layer thickness, corrosion condition test) and concrete (carbonation depth, alkali content and chloride ion content related to strength grade and durability); for the material detection type, it is mainly to check Non-destructive or minimally destructive testing of bridge structural materials is also a current key research area; structural data mainly refers to the process of mastering the original construction technology, structural design and structural repair and maintenance history of the bridge, so as to analyze the bridge according to relevant specifications as standards quality status. In addition, in order to improve inspection efficiency, advanced high-tech instruments for bridge deck inspection can be purchased, such as lidar, which is used to measure the entire bridge; dual-band infrared automatic temperature imaging system, which can be used to inspect the bridge deck; ground penetrating radar imaging system , can be used to detect bridge decks, etc.
2.2 Technology for detecting bridge operating conditions and bearing capacity
To judge the bearing capacity of a bridge alone, the static load test method can be used, which can measure deformation and deflection , strain, cracks and other parameters related to the performance of the bridge structure, so as to analyze the strength, stiffness and crack resistance of the structure and judge it. To comprehensively consider the operating conditions and load-bearing capacity of the bridge, the dynamic performance of the bridge structure can generally be studied through dynamic load testing methods. The specific inspection points are: If you want to examine the safety and economic performance of the bridge design, you can start by determining the vehicle load. The important technical parameter that can be checked is the dynamic coefficient. In the past, the main purpose of dynamic testing was to consider the natural vibration frequency of the bridge, and its key parameter was the impact coefficient. In the practice process of highway engineering testing. The main contents of dynamic testing include: determining the natural vibration characteristics such as the natural frequency, vibration shape and damping characteristics of the bridge span structure; measuring the forced vibration frequency, impact coefficient, dynamic displacement and dynamic stress of the bridge span structure under vehicle load. characteristic.
However, if the occurrence of structural losses will inevitably lead to changes in structural parameters such as stiffness, damping, and internal loads, and reasonable estimation of these changes will provide a quantitative method for the evaluation of the structural operating status.
The extraction of bridge vibration modal characteristic parameter change information can be achieved by detecting different positions of the bridge before and after structural damage, and then from the information recorded at these measuring points, thereby assessing the degree of structural damage. Location and type of structural damage. In general, bridge vibration modes can be obtained through conventional experimental modal analysis testing techniques. In short, to evaluate changes in bridge structural parameters, in addition to traditional static and dynamic load-bearing tests, it can also be analyzed through changes in bridge vibration modes. The vibration method is the basic technology for bridge operation detection. There is also the design of the test system, which can detect the performance of the instrument and determine the characteristics of the sensor used. The test instruments involved in the dynamic load test mainly include optical oscilloscopes, signal amplifiers, test sensors, tape recorders and digital signal processors.
2.3 Detection technology when detailed bridge information cannot be obtained
Some engineering data may not be able to obtain more comprehensive data due to various reasons. In this case, we Structural performance testing technology can be considered. Commonly used testing technologies include static testing and dynamic testing, which can accurately reflect the structural stress performance. The static load test of concrete bridges generally requires the following tests. In the past, bridge inspection work mainly relied on on-site visual inspection and dynamic and static load tests by inspectors, combined with a variety of inspection technologies, such as ultrasonic detection, corrosion experiments, concrete hardness tests and other traditional inspection methods. Although the key components and nodes of the bridge can be reasonably judged However, it is difficult to meet the overall performance evaluation needs such as the bridge's operating health, the safety of the bridge structure, and its lifespan. With the continuous development of economy and technology, especially the development of communication and sensing technology, more advanced detection technology, such as non-destructive testing technology, has been provided for bridge detection work, making the detection technology more systematic, fast and intelligent. Development, to a certain extent, meets the needs of modern highway bridge inspection.
The bridge vibration modes mentioned above are expected to provide new detection technology for evaluating the safety performance of bridges from an overall perspective. In addition, bridge structure damage identification and detection technologies currently include wavelet analysis damage identification method and neural network damage identification method. The former can directly extract information useful for operations, and can also be applied to damage in signal-noise separation, singular signal detection, frequency band analysis, etc. Identification, and because wavelets are suitable for analyzing unbalanced signals, this type of detection technology can be used as an ideal tool for signal processing in damage identification; the main function of the latter is mainly to construct the network, through the difference between the output of the system and the output of the network To test the extent of damage, the data comes from vibration measurements of non-damage systems.
2.4 Acoustic detection technology, which is relatively simple to detect bridge damage
As can be seen from the previous analysis, the current detection technology has some shortcomings. The most common detection technology for highway bridges in my country is still There is sonic detection technology. Because it is simple and convenient to use, it has been widely used in recent years. The working process of this type of bridge inspection technology: From the road surface and the ground of the bridge, the sound waves reflected from the road surface are received through corresponding receiving instruments, and through a series of information processing measures, the inspection technicians are provided with the internal damage status of the bridge. Take timely maintenance techniques. It is mainly based on the characteristics of the internal wave characteristic parameters and the mechanical parameters of the object, and obtains information such as the frequency, wave speed and waveform of the propagating elastic wave. Combined with other analysis techniques, the bridge damage condition can be judged. In addition, mechanical detection technology. Mechanical testing instruments are the same as acoustic wave detection technology. They have simple working principles, easy and affordable operation, long service life, and strong ability to adapt to the surrounding environment. However, they also have obvious shortcomings, such as limited amplification capability, low sensitivity, and relatively low sensitivity. bulky.
2.5 Learn from the detection technology that foreign countries are currently paying attention to
Currently, foreign parties have carried out research on bridge management systems and quantitative non-destructive testing methods, that is, by using the forced vibration response method Quantitative testing technology uses a laser vibrometer to measure cable forces and evaluate the bridge substructure.
Our country has always advocated the introduction of foreign advanced technologies. This article summarizes its main technologies:
(1) Advanced fatigue crack detection and assessment system, involving wireless strain measurement system for bridge cracks, passive fatigue load measurement equipment, Portable acoustic emission systems, new ultrasonic and electromagnetic acoustic emission sensors, etc., currently based on this, a broadband E detector is capable of generating (signals) and detecting fatigue cracks under different stress modes;
( 2) Advanced corrosion detection technology, such as buried corrosion micro-sensors that detect pre-tensioning grouting gaps and magnetic leakage detection technology;
(3) Advanced bridge deck detection systems, such as dual-band remote Infrared thermal imaging system;
(4) It has advanced bridge testing and health monitoring systems, such as steel sensors that measure bridge overload.
3. Conclusion
In summary, dynamic and static load tests and on-site visual inspection by inspectors are traditional bridge inspection methods. With the development of science and technology, detection of damage caused by The experimental modal analysis method of structural parameter changes to evaluate damage reflects the strain modal measurement of the inherent characteristics of the structure. This article believes that to evaluate the degree of bridge structural damage, among the measurement and evaluation methods discussed, the vibration modal measurement method is better; at the same time, the stress and strain parameters among the structural damage sensitive parameters are the development trends of highway bridge detection technology, but this aspect The detection technology still needs more practice and exploration; vibration displacement detection technology can be considered as a new way to determine the mechanical state of the bridge, which can well make up for the shortcomings of the strain measurement system. In addition, our country should also combine multiple detection technologies in practice to make the detection results more scientific and comprehensive.
The above is collected and compiled by Zhongda Consulting
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