1, overview
1. 1 Definition of bridge structure inspection
Bridge structural inspection is mainly to investigate the technical status of bridges, that is, the nature, location, severity and development trend of bridge defects and injuries, find out the main causes of defects and injuries, analyze and evaluate their impact on bridge quality and service bearing capacity, and provide reliable technical data and basis for bridge maintenance and reinforcement design. The work that the bridge inspection room must do before the maintenance, repair and reinforcement of its bridge is a reliable guarantee to determine whether the maintenance and reinforcement scheme is feasible and correct, and it is also an indispensable and important link in bridge evaluation, maintenance, repair and reinforcement.
1.2 bridge structure types in Guizhou
Guizhou is a typical karst landform, which can be divided into three types: plateau mountain, hill and basin. Rivers in Guizhou are located in the crisscross zone between the upper reaches of the Yangtze River and the Pearl River. The water system of the whole province is divided into three parts along the terrain: west, middle, north and southeast. Therefore, there are relatively many types of bridges in mountainous areas, and their structures are relatively complex. There are mainly beam bridges (mainly T-beams and continuous box girders), slab bridges, cable-stayed bridges, reinforced concrete arch bridges, suspension bridges and stone arch bridges.
2, bridge engineering detection method
With the increasing traffic density and vehicle load in China, bridges will inevitably be damaged due to overload and other factors in long-term use. If maintenance is not carried out and some reinforcement measures are taken, the durability and bearing capacity of the bridge will be reduced, which may seriously lead to traffic accidents. This paper will further discuss the common points and methods of bridge engineering detection.
2. 1 Bridge appearance inspection method and key points
Appearance inspection includes the measurement of geometric dimensions of the whole and local structure of the bridge, the inspection and measurement of structural diseases, etc. Different types of bridges have different inspection emphases. Generally speaking, bridges can be divided into three parts:
(1) superstructure, mainly refers to the main girder in the beam bridge;
(2) substructure, generally including foundation and pile cap, arch crack, pier, pile and abutment displacement, etc.
(3) Accessory structures should generally focus on bridge deck pavement, expansion joints, railings, etc. , and other inspection points, such as oblique cracks at the end of the beam bridge and cracks and deflection in the midspan. For reinforced concrete bridge type, it is mainly to detect steel bars (test of protective layer thickness and corrosion conditions) and concrete (alkali content and chlorine content related to carbonation depth, strength grade and durability); For the types of material testing, it is mainly to check the nondestructive or slight damage detection of bridge structure materials, which is also the key research field at present; Structural information is mainly to master the original construction technology, structural design and structural maintenance history of the bridge, so as to analyze the quality of the bridge according to relevant specifications. In addition, in order to improve the detection efficiency, you can buy advanced high-tech instruments for bridge deck detection, such as laser radar, for the whole bridge measurement; Dual-band infrared automatic temperature imaging system can be used for bridge deck detection; Ground penetrating radar imaging system can be used to detect bridge deck, etc.
2.2 Bridge operation and bearing capacity detection technology
From the aspect of judging the bearing capacity of the bridge, static load test can be used to analyze the strength, stiffness and crack resistance of the structure by measuring the performance-related parameters such as deformation, deflection, strain and crack of the bridge structure. In order to comprehensively consider the running state and bearing capacity of the bridge, the dynamic performance of the bridge structure can be studied by dynamic load test. The specific detection points are as follows: If the safety and economy of bridge design are to be investigated, the vehicle load manpower can be determined, and the important technical parameter to be checked is the dynamic coefficient. In the past, the main purpose of dynamic test was to consider the natural frequency of the bridge, and the key parameter was the impact coefficient. The main contents of dynamic test include: measuring the natural vibration characteristics of bridge-span structure, such as natural frequency, vibration mode and damping characteristics; The forced vibration characteristics of bridge-span structure under vehicle load, such as forced vibration frequency, impact coefficient, dynamic displacement and dynamic stress, are measured. However, if the structural loss occurs, it will inevitably lead to changes in structural parameters such as stiffness, damping and internal load, and reasonable estimation of these changes will provide a quantitative method for the evaluation of structural operation state.
By detecting the different positions of the bridge before and after structural damage, we can extract the change information of the characteristic parameters of the vibration mode of the bridge, and then realize the information recorded from these measuring points, so as to evaluate the degree, position and type of structural damage. Generally speaking, the vibration modes of bridges can be obtained by conventional experimental modal analysis and testing techniques. In short, in order to evaluate the changes of bridge structural parameters, in addition to the traditional static and dynamic load tests, the changes of bridge vibration modes can also be analyzed, among which vibration method is the basic technology of bridge operation detection. There is also the design of the test system, which can detect the performance of the instrument and determine it by using the characteristics of the sensor. The test instruments involved in dynamic load test mainly include optical oscilloscope, signal amplifier, test sensor, tape recorder, digital signal processor and so on.
2.3 Detection technology in the case that detailed information of bridges cannot be obtained.
Some engineering data may be unable to obtain more comprehensive data for various reasons. In this case, the structural performance state detection technology can be considered. The two commonly used detection technologies are static test and dynamic test, which can accurately reflect the structural mechanical performance state. The static load test of concrete bridge generally requires the following test contents. In the past, bridge inspection mainly relied on visual inspection and static and dynamic load test by inspectors. Combined with various traditional detection methods, such as ultrasonic testing, corrosion test and concrete hardness test, although the damage degree of key components and nodes of the bridge can be reasonably judged, it is difficult to meet the evaluation requirements of the overall performance of the bridge, such as operational health, structural safety and service life. With the continuous development of economy and technology, especially the development of communication and sensing technology, more advanced detection technologies, such as nondestructive detection technology, are provided for bridge detection, which makes the detection technology develop into systematization, rapidity and intelligence, and meets the needs of modern highway bridge detection to some extent.
The above vibration modes of the bridge are expected to provide a new detection technology for the evaluation of the overall safety performance of the bridge. In addition, there are two kinds of bridge structure damage identification detection technologies: wavelet analysis damage identification method and neural network damage identification method. The former can directly extract useful information for operation, and can also be applied to signal-noise separation, singular signal detection and damage identification in frequency band analysis. Because wavelet is suitable for analyzing unbalanced signals, this detection technology can be used as an ideal tool for signal processing in damage identification. The main function of the latter is to construct a network and test the damage degree by the difference between the output of the system and the output of the network. The data comes from vibration measurement of non-destructive system.
2.4 Bridge damage detection is a relatively simple acoustic detection technology.
From the previous analysis, it can be seen that the existing detection technology has some shortcomings, and acoustic wave detection technology is more common in highway bridge detection technology in China. Because it is simple, convenient and close to use.
It has been widely used in recent years. The working process of this kind of bridge detection technology: from the pavement and ground of the bridge, the sound waves reflected from the pavement are received by corresponding receiving instruments, and a series of information processing measures are taken, so as to provide the detection technicians with the internal damage of the bridge and take timely maintenance technology. It is mainly based on the characteristics of wave characteristic parameters and mechanical parameters in objects, from which information such as frequency, wave velocity and waveform of propagating elastic waves can be obtained, and combined with other analysis techniques, the damage state of bridges can be judged. In addition, mechanical detection technology. Like acoustic wave detection technology, mechanical detection instrument has simple working principle, convenient and economical operation, long service life and strong ability to adapt to the surrounding environment, but it also has obvious shortcomings, such as limited amplification ability, low sensitivity and relatively heavy.
2.5 Learn from the detection technology that foreign countries are currently concerned about.
At present, foreign countries have begun to study the nondestructive testing method combining bridge management system with quantification, that is, the forced vibration response method is used to measure the cable force of cable-stayed bridges, and the laser vibrometer is used to evaluate the bridge substructure. China has always advocated the introduction of foreign advanced technology. This paper summarizes its main technologies:
(1) Advanced fatigue crack detection and evaluation system, involving wireless strain measurement system for bridge cracks, passive fatigue load measurement equipment, portable acoustic emission system, new ultrasonic and electromagnetic acoustic emission sensors, etc. At present, based on this, a broadband E- detector is designed to generate (signal) and detect fatigue cracks under different stress modes.
(2) Advanced corrosion detection technology, such as embedded corrosion microsensor and magnetic flux leakage detection technology for detecting the pre-tensioned grouting gap;
(3) Advanced bridge deck detection system, such as dual-band far infrared thermal imaging system;
(4) Have advanced bridge detection and health monitoring systems, such as steel sensors for measuring bridge overload.
3. Conclusion
To sum up, static and dynamic load test and on-site visual inspection by inspectors are traditional bridge inspection methods. With the development of science and technology, experimental modal analysis method has gradually appeared, which can evaluate the damage by detecting the changes of structural parameters caused by damage, thus reflecting the inherent characteristics of the structure. This paper holds that vibration modal measurement is the best method to evaluate the damage degree of bridge structure. At the same time, the stress-strain parameter among the structural damage sensitive parameters is the development trend of highway bridge detection technology, but this detection technology needs more practice and exploration; The new method to determine the mechanical state of bridge can consider vibration displacement detection technology, which can make up for the deficiency of strain measurement system. In addition, China should combine various detection technologies in practice to make the detection effect more scientific and comprehensive.
The above are collected and sorted by Zhong Da Consulting Company.
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