The scope of civil engineering design is relatively wide, including road engineering, construction engineering, underground engineering, bridge engineering and so on. With the gradual expansion of the scale of civil engineering construction, people pay more and more attention to its safety. If there are safety and quality problems, it will lead to safety accidents, which will not only endanger people's lives and property, but also bring huge economic losses to the country. Therefore, it is very important to do well the safety design of civil engineering structures.
1 overview of structural safety in civil engineering
The safety of civil engineering structure refers to the ability of the structure and its components to prevent damage and collapse and protect personnel and equipment from damage under various possible external effects such as loads. 1. 1 External action of structure and external action of structural design (1) General action, accidental action, environmental action or environmental impact (such as corrosion of steel bars and concrete) that lead to deterioration of structural materials. (2) The structural design adopts the limit state design method. During its design service life, the structure and its components must have appropriate safety and reliability, and should meet the following three basic functional requirements: ① meet the applicability requirements for normal use under general or environmental effects; (2) It has enough bearing capacity to resist serious damage such as collapse under possible general and accidental actions; (3) Under the action of accidental disasters that can or can't be met or under the influence of main human beings, the structure should not have serious destructive consequences disproportionate to its initial causes, that is, the structure must have overall firmness and stability.
(3) For structural design, to ensure the safety of the structure, the following points must be achieved: ① Under the possible general action and the specified accidental action, every component of the structure (such as beam, plate, column and their connections) has sufficient strength and stability, that is, the safety of the component in carrying capacity; (2) The structure must have overall firmness, and no matter natural or man-made disasters, the structure should not have disproportionately serious damage consequences; (3) Under the action of environment, the deterioration of structural materials should be controlled within an acceptable range. Note: For the design of concrete structures, the main limit states are the bearing capacity limit state (corresponding to the safety of members), deformation limit state and crack limit state in normal use.
1.2 Safe setting level of bearing capacity of members (1) In the structural design code, the general calculation formula of ultimate state design of bearing capacity is: the standard value of material strength, and the limit state design method of reliability or safety factor is generally adopted as the standard value at present. (2) Partial coefficient and safety factor Under the general load, the partial coefficient of material strength specified in Chinese codes is about 10~ 15% lower than the corresponding safety factor in Britain and America. From the table 1, it can be found that the safety setting level of bearing capacity of members in China structural design code is the lowest in the world. Under the unexpected load, Chinese codes only require that the necessary overall stability can be maintained during and after the accidents specified in the design (except for buildings with special purposes), and only stipulate the requirements of earthquake action and fire prevention, without considering the possible explosion, impact and serious human error, and how to mitigate the disastrous consequences when an earthquake with intensity greater than that specified in the code occurs.
1.3 overall firmness of the structure For the overall firmness of the structure, China's code has not yet put forward specific analysis methods and standards, and can only be guaranteed by reasonable structural scheme and layout and reliable structural measures. 1.4 environmental effects The key content in the Code for Design and Construction of Civil Building Structures in China is the structural strength requirements of structures under various loads, but insufficient attention is paid to the structural strength requirements under environmental effects, such as dry and wet, freezing and thawing, and the erosion of harmful chemical media in water and soil around the project. In structural design, attention should be paid to prevent the corrosion of concrete and steel bars and prevent the concrete from cracking.
2. The current safety problems of civil engineering structure design
2. 1 Code for Design Structure of Civil Engineering has a low safety level. At present, there are still many hidden dangers in the design of civil structures in China. Some civil structures will have some quality problems after being used for a period of time, such as cracks and deformation in the building wall. In some foreign countries, some buildings or bridges have a history of hundreds of years, but they are well preserved and basically have no major quality problems. The main reason for the above phenomenon is that compared with some foreign countries, the safety setting level of civil structures in China is relatively low. At present, the seismic fortification targets stipulated in China's seismic design code are that small earthquakes are not bad, moderate earthquakes can be repaired, and large earthquakes cannot collapse. The structural design under this goal can only ensure that the building is intact under small earthquakes, but it is difficult to ensure its structural safety under large earthquakes.
2.2 The stability of the structural system in civil engineering design is poor. Only by ensuring the stability of the structure can the safety of the structure be improved. If the structure has high stability, even if the building is damaged to a certain extent, it will not damage the overall structure of the building. However, as far as the current situation in China is concerned, the stability of civil engineering structures is still relatively low, and the stability design technology of civil engineering structures is still relatively lacking, which makes civil structures collapse and cause certain personal injuries. The collapse of houses caused by Yushu earthquake has always warned us that it is very important to enhance the stability of civil engineering.
2.3 The cross-sectional area design of frame columns is not standardized. In some areas, the requirements for seismic grade of buildings are relatively low, because structural designers usually design smaller cross-sectional areas of frame columns in the design process. In order to control economic indicators, some structural designers try to reduce the number of frame columns in the structural system and increase the span of beams. However, in order to meet the design requirements, the stiffness of beams is generally relatively large, and there will be strong beams and weak columns, which violates the design concept of strong columns and weak beams. Once the strong beam and weak column encounter external forces such as extreme weather or earthquake, it is easy to cause cracks in the core area of the building beam and column, which greatly shortens the service life of the building. It may even lead to the collapse of buildings and seriously endanger people's lives and property.
3 main measures to improve the safety of civil engineering structure design
3. 1 The design method should be optimized. With the rapid development of China's economy and the gradual acceleration of civil engineering construction, we must pay more attention to the safety of civil structures and formulate a feasible new standard system for the construction industry according to the current actual situation. In the process of structural design, relevant designers should design in strict accordance with relevant national standards to maximize the safety and stability of the structure. At the same time, the design methods adopted should not be limited to linear small earthquake calculation and moderate earthquake method. We must check each project for moderate earthquake and take effective reinforcement measures for easily damaged structural members to ensure that the structural system remains intact under moderate earthquake. In addition, we should combine the actual needs of our country, improve the relevant technical standards, and learn from some foreign technologies and concepts to improve the safety of civil engineering structure design in our country.
3.2 Attach importance to the cultivation of safety responsibility concept of designers. Designers play an important role in the structural design of civil engineering and have an important impact on the safety of the structure. In the process of result design, designers are not only required to have solid theoretical knowledge and professional skills. The concept of safety responsibility and safety awareness should also be required. Designers must make repeated calculations in the design process to ensure that every data is well documented. In order to improve the safety awareness and professional skills of designers, we should strengthen the training and learning of designers, and require designers to constantly sum up experience to ensure the high quality of design.
3.3 Strengthening scientific research, promoting innovation and improving the level of structural design can make the designed products have higher quality and more reasonable structural forms, so we should constantly strengthen innovation and development. As structural designers, we can't be satisfied with the status quo. We must apply the results to practical projects through a lot of research and repeated calculations. Only in this way can the finished product be safer and more reliable.
3.4 Strictly control the use conditions of buildings. After the civil structure is delivered for use, it needs to be handed over to the responsible party of the building to control the use requirements of the building and require the building to be used according to the design conditions. It is forbidden to use beyond the design standard to improve the reliability of the structure.
3.5 Do a good job in internal force combination design. The key point of seismic design of civil structures is internal force combination design. In the design of internal force combination, materials with good seismic performance should be selected based on the seismic coefficient of structural bearing capacity, and the seismic coefficient of structural bearing capacity should be adjusted according to factors such as bending beam, eccentric compression column, shear force and bearing capacity of members, so as to improve the bearing capacity of civil structures.
4 conclusion
To sum up, the safety of civil engineering structure is very important, which directly affects the quality and service life of the project. In the process of structural design, designers must strengthen safety awareness, apply reasonable design methods and sum up relevant experience to ensure the safety and durability of structural design.
This paper introduces the content of "Problems and Strategies in Structural Design of Civil Engineering". Welcome to Zhong Da for more information.
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