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Present situation and trend analysis of building structure detection

Ren 1, 2 (1. Shangyu Construction Engineering Quality Testing Center; 2. Zhejiang Zhongfu Construction Group Co., Ltd., Shangyu, Zhejiang 3 12300)

2009-3-30

Abstract: With the continuous development of the construction industry, people pay more and more attention to the detection of building structures. Based on this, this paper analyzes the present situation and trend of building structure detection. Firstly, the engineering background of building structure detection is introduced, then the identification method and detection technology are analyzed, and finally the standards and methods of building structure detection and identification are analyzed.

Keywords: building structure; Detection technology; Identification method

China Library Classification Number: TU3 12 Document Identification Number: A Document Number:1009-2374 (2009) 03-0135-02.

First, the engineering background of building structure detection

In the 1970s, the development speed of building inspection, appraisal, maintenance and renovation began to accelerate, and countries correspondingly increased the investment proportion of building maintenance and renovation, and the industry scale expanded rapidly. Building inspection, appraisal, maintenance and renovation industries can play an increasingly prominent role in today's economic construction and social development, which is related to the following reasons:

(a) Buildings are vulnerable to all kinds of disasters.

1. earthquake. This is by far the most destructive disaster to buildings. There are about 700, 200 and 30 counties and cities in China with basic fortification intensity of 7 degrees, 8 degrees and above respectively. 46% of the cities are located in the earthquake zone, and 2/3 of the big cities are located in the earthquake zone.

2. Fire. Among all kinds of fires, building fires account for about 80%. On average, there are about 30 thousand building fires in China every year, and the direct economic loss is about 654.38+0 billion yuan.

3. Flood. The coastline of Chinese mainland is 1.800 km, and more than 70% of the cities are located in coastal areas. The direct economic losses caused by marine disasters exceed 2 billion yuan every year.

4. Wind disaster. More than 15% of the world's population lives in areas at risk of tropical storms, including the southeastern United States, Japanese, Philippine and China coastal areas.

In addition, there are disasters such as explosions and ice disasters. These disasters will leave a large number of damaged or damaged buildings, which need to be repaired and strengthened by technical means, and reliability testing, appraisal and maintenance will be carried out.

(B) Engineering construction quality accidents are hard to avoid

In the early days of economic system reform in 1980s. The scale of engineering construction is expanding rapidly, but the management system is not perfect, the technical force is weak, and the quality of engineering construction is seriously declining. Since the 1990s, China's national economy has developed rapidly, the project construction has maintained a large scale, and the construction team has expanded rapidly. However, the construction industry is in a period of transition to a market economy, the legal system is not perfect, irregularities and improper behaviors are prominent in market competition, and the quality of engineering construction has always been concerned by people.

Quality accidents in engineering construction also need to be detected, analyzed and evaluated by technical means, and handled accordingly.

(3) The functions of old buildings are relatively backward.

With the development of social economy and culture, people's requirements for living and working environment are also changing, especially for building space, lighting, ventilation and energy saving, which will lead to the functional standards of a considerable number of old buildings lagging behind.

The functional lag of a certain number of buildings is the inevitable result of social development and scientific and technological progress, and it is a common problem that must be faced at any time. One of the solutions is to carry out technical transformation after testing, analyzing and appraising the old buildings.

Second, the identification method and detection technology

recognition methods

Generally speaking, there are three valuation methods for buildings: traditional empirical method, practical valuation method and probability valuation method.

1. Traditional empirical method. By experienced experts, through on-site observation and simple calculation and analysis, on the basis of the original design code, according to personal professional knowledge and engineering experience, the reliability of the building is directly evaluated. The appraisal procedure of this method is simple, but it is difficult for appraisers to obtain more accurate and complete data and information, and it is also difficult to comprehensively analyze the performance and state of the structure. Therefore, the evaluation process is not systematic, and the judgment of the reliability level of the building is subjective, and the appraisal conclusions often vary from person to person, while the engineering treatment schemes are mostly conservative, resulting in waste.

2. Practical identification methods. The building and its environment are carefully investigated, inspected and tested by various detection methods, and the performance and state of the building are analyzed by computer technology and other related technologies and methods, and the reasons for the problems in the building are comprehensively analyzed. According to the current standards and codes, and in accordance with the unified appraisal procedures and standards, the reliability level of buildings is comprehensively evaluated from two aspects: safety and applicability. Compared with the traditional empirical method, this method is scientific in appraisal process, can accurately judge the reliability level of buildings, and can provide reliable technical basis for the decision-making of building maintenance, reinforcement and reconstruction schemes.

3. Probability appraisal method. On the basis of practical appraisal method, the uncertain factors affecting the reliability of specific buildings are further analyzed by statistical inference method, and the reliability level of buildings is evaluated more directly by reliability theory. Probability appraisal method is aimed at specific existing buildings, and through the collection and analysis of building and environment information, the reliability level of buildings is evaluated, and the evaluation conclusion is more in line with the actual situation of specific buildings.

(2) Detection technology

Detection technology is an important engineering technology on which building reliability appraisal depends. At present, the development of building detection technology presents the following trends.

1. The detection content tends to be systematic and in-depth. In addition, there are material strength, component size and damage, structural deformation and displacement. At present, the detection technology has been extended to other geometric, mechanical and physicochemical properties of materials, components and structures, such as water content, cement content, chloride ion content, PH value and impermeability of concrete materials, location, diameter and corrosion state of steel bars in concrete, development of cracks and defects in components, surface temperature of components, working stress and static state of components. These contents are not only related to the safety and applicability of buildings, but also related to the durability and service life of buildings. The perfection of the test content will help people to understand and master the performance and condition of the building more comprehensively and deeply, and provide more sufficient basis for the reliability appraisal of the building.

2. The detection methods are increasingly advanced and rich. The detection methods of buildings have developed rapidly, and many technologies are quite mature, which have entered practical projects, such as rebound method, core drilling method, ultrasonic rebound synthesis method and pull-out method after installation, ultrasonic method for detecting steel and weld defects, ultrasonic method, ray method, magnetic particle method, infiltration method and eddy current method for detecting surface stability of components. At present, there are still many mechanical, physical and chemical detection methods in research and development, among which the penetration resistance method and nail pressing method for detecting concrete strength, acoustic emission method for monitoring the development of concrete cracks and defects and detecting concrete strength and working stress, electromagnetic method and radiation method for detecting concrete defects and rebar positions, infrared photography method for detecting concrete defects, resistance method, capacitance method and neutron scattering method for detecting concrete moisture content, and neutron activation method for detecting concrete cement content and rebar corrosion.

3. The test instrument is integrated and intelligent. More and more testing instruments with complete functions and simple operation have been developed and applied, such as dynamic measuring equipment that can automatically analyze buildings in time domain and frequency domain, infrared thermal imager that can detect concrete cracks and damaged parts according to temperature difference, potential difference steel corrosion detector that uses wheel electrodes to detect steel corrosion in concrete, and color image analysis system that can automatically determine the distribution, width and length of concrete cracks. The integration and intelligence of test instruments not only improve the efficiency of test, but also reduce human errors and mistakes in test analysis to a great extent.

Third, the identification standard.

Most existing buildings are designed according to the past standards and codes, and the implied reliability level is different from the current standards and codes. Whether the reliability meets the requirements should be based on the currently recognized reliability index limit, and the methods of structural mechanical analysis and component checking calculation should be established according to more advanced design ideas to ensure the reliability of buildings meets the current requirements.

A more reasonable method is to give the evaluation criteria some flexibility; If the reliability index of the existing building is only slightly lower than the limit value of the current reliability index, it should be accepted in principle without reinforcement or local treatment; What is unacceptable is those buildings with large differences in reliability indicators, which are the key targets of reinforcement and transformation.

Fourth, the methods of detection and identification

The object of building reliability appraisal is a realistic and specific spatial entity, and its environment provides valuable historical and current information, effectively describing the past change track and current characteristics of buildings and environment. For example, the current strength of concrete materials, the current use of components, the disasters that the structure has suffered, and the actual load of the roof structure layer. It is of great significance to reasonably predict the future performance and various functions of buildings. Building reliability appraisal should be based on the information of the building and the environment itself, combined with the testing items, which is a remarkable feature of building reliability appraisal.

Because the building is a spatial entity, it has been used for a certain period of time, and the actual performance of structural materials, structural components and structural systems has been tested by history in the process of use, which is manifested to some extent through the actual state of the building. Such as deformation and appearance. It can directly determine whether the reliability of the building meets the requirements within the target service life, and it is an evaluation method based on state evaluation. In some specific cases, the evaluation method based on load test can also be adopted, that is, the deflection and crack width of structural members can be directly determined through on-site or indoor load tests. Whether the crack resistance or bearing capacity meets the requirements. These two evaluation methods are completely based on the empirical information provided by buildings and environment, and are unique methods for building reliability evaluation.

In a word, in the reliability appraisal of existing buildings, the target service life and preconditions should be defined, and the possible changes of buildings and environment in the future should be taken as the benchmark, and the evaluation criteria should be given some flexibility. The reliability level of buildings should be evaluated based on performance analysis, state evaluation or load test.

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Wu Huimin. On-site detection technology of structural concrete [M]. Changsha: Hunan University Press, 1988.

[3] Zhou Yu and Liu Yihong. Engineering structure inspection [M]. Beijing: Peking University Publishing House, 2007.