A, the safety of civil engineering structure

Structural safety is the ability of structure to prevent collapse and the most important quality index of structural engineering. The safety of structural engineering mainly depends on the design and construction level of the structure, and it is also related to the correct use (maintenance and inspection) of the structure, and then to the reasonable setting and application of civil engineering regulations and technical standards (specifications, regulations, procedures, etc.). ).

1. Safety setting level of China structural design code.

For the design of structural engineering, the safety of structure is mainly reflected in the safety of bearing capacity of structural members, the overall firmness of structure and the durability of structure. Generally speaking, the design standards of civil structures such as buildings and bridges in China are far lower than similar foreign codes.

The safety setting level is 1. 1 component bearing capacity.

The two factors that have the greatest relationship with the safety level of structural members are: according to the 1) code, how much load (load standard value) the structure needs to bear, such as the same office building. Starting from 1959, China's code stipulates that the live load borne by the floor is per square meter 150 kg (it has been determined to be changed back to 200 kg in the new code), while it is 2400 kg in the United States and Britain. 2) The load subentry coefficient and the material strength subentry coefficient specified in the specification, the former is the coefficient to enlarge the standard value of load when calculating and determining the effect of load on structural members, and the latter is the coefficient to reduce the standard value of structural members when calculating and determining the inherent bearing capacity of structural members. The coefficients expressed by these parameters reflect the safety degree of structural members under a given standard load, which is called safety factor in the design method of safety factor (such as the design code of highway bridges and culverts in China), reflecting the need of safety reserve; In the reliability design method (such as the code for design of building structures in China), it is called subentry coefficient, which embodies a certain nominal failure probability or reliability index. The greater the safety factor or subentry factor, the higher the safety degree. The subentry coefficients of live load and dead load (such as structural self-weight) are 1.4 and 1.2 in China's code for design of building structures, while they are 1.7 and 1.4 in America and 1.6 and1. In this way, when designing an office building according to Chinese standards, the floor design load (the product of standard load value and partial load coefficient) is only about 52% (considering the live load of personnel and facilities) and 85% (the dead load of the structure) of Britain and America. The structural design of some developing countries mostly refers to the norms of developed countries, just as the structural design methods of China before liberation and in the early days of the founding of the People's Republic of China refer to American norms. As for China's Hongkong and Taiwan Province provinces, they are still based on the standards of Britain and the United States respectively. What needs to be explained here is that the standard value of live load of other buildings is not as big as that of foreign office buildings, apartments and dormitories. The gap between different materials and different types of structures in safety setting level is different internationally. For example, the gap between steel structures may be relatively small.

The situation of highway bridge structure is similar to that of building structure. In addition to the vehicle-mounted standards, the safety factor of load members (the vehicle-mounted standard in China is 1.4, which is about 25% lower than the internationally famous American AASHTO code 1.75) and the safety factor of material strength members are low.

Although the safety reserve set in China's design code is low, the material consumption of some projects is higher than that of similar projects abroad. The main problem here is conservative design and lack of innovation in structural scheme, material selection, analysis and calculation, structural structure and so on.

1.2 overall firmness of the structure

In addition to the sufficient bearing capacity of structural members, the structure should also have overall firmness. The overall soundness of a structure refers to the ability that local destruction of a certain part of the structure will not lead to large-scale continuous destruction and collapse, or that the structure should not have destructive consequences disproportionate to its causes. The overall stability of the structure mainly depends on the good ductility and necessary redundancy of the structure, which can be used to deal with the disaster consequences caused by earthquake, explosion and other disaster loads or human errors, and can reduce disaster losses. The huge casualties caused by the Tangshan earthquake are closely related to the lack of overall stability of local housing structures. A vicious explosion occurred in 200 1 Shijiazhuang, and the wall of a residential building was partially destroyed due to the explosion of soil explosives, resulting in the continuous collapse of the whole building, which is also a sign that the house design is not solid enough.

Persistent security of 1.3 structure

China's Code for Structural Design and Construction of Civil Buildings focuses on the structural strength requirements under various loads, but relatively little consideration is given to the durability requirements under environmental factors (such as atmospheric erosion such as dry and wet, freezing and thawing, and the erosion of harmful chemical media in water and soil around the project). The severity of structural safety accidents caused by steel corrosion or concrete corrosion in concrete structures is far greater than the harm caused by low safety level of bearing capacity of structural members, so special attention must be paid to this problem. Some durability-related requirements stipulated in China Code, such as the minimum thickness of concrete cover to protect steel bars from corrosion and the minimum strength grade of concrete, are obviously lower than those in foreign codes. Destroying the safety of the bearing capacity of the structure is only one of the consequences of insufficient durability; Improving the safety setting level of bearing capacity of structural members is also beneficial to the durability and service life of structures in some cases.

2. Different opinions on adjusting the level of structural safety setting

The low level of safety setting in China's structural design code is related to the long-term lack of economic and planning system in China after the founding of the People's Republic of China. However, the low safety level of civil engineering structure can basically meet the needs of production and life at that time, and it has passed the long-term test, which is a great achievement made by domestic civil engineering technicians through great efforts; However, due to the low safety reserve, the ability to resist unexpected effects is relatively insufficient. If the safety setting level is properly improved, it will help to reduce the frequency of accidents and improve the ability of the project to resist disasters. A large number of engineering safety accidents in China are mainly caused by corruption and mismanagement in management and serious human errors. Now it is proposed to re-examine the safety setting level of structures, mainly based on the changes in the objective situation, because the infrastructure construction we are engaged in now should lay the foundation for future modernization and meet the needs of the development of people's production and living standards in the next few decades and hundreds of years, and some civil structures, such as commercial houses, should meet the needs of commodity attributes under the conditions of market economy. In recent years, there have been several discussions on the setting level of building structural safety in China, and there are great differences on how to adjust it. These different opinions are also reflected in this science and technology forum:

1) thinks that the safety setting level in China's current code is sufficient and has been proved by long-term practice, but there is no such experience abroad. This successful experience of our country must not be easily lost, and we cannot follow the high standards of Britain and the United States in terms of safety; A high degree of safety is a waste, and there is no need to change it as a whole except for individual adjustments.

2) It is considered that although the safety setting level in China's codes is not high, most of the tens of billions of square meters of buildings built on this basis are still in safe use under the "three normal" conditions of normal design, normal construction and normal use, which shows that the standards stipulated in these codes are still applicable; However, the ideal "three normals" are difficult to achieve. At the same time, in order to narrow the gap with the international advanced level and meet the needs of sustainable development and durability improvement, the safety setting level of the structure should be appropriately improved under the condition of market economy with improved material supply conditions. This improvement can only be moderate, because China is still a developing country.

3) It is considered that the standard safety setting level in China should be generally close to the international level and need to be greatly improved. This is because with the continuous improvement of China's economic development and living standards, the consequences of risk loss caused by accidents in civil engineering, especially major infrastructure projects, will become more and more serious, and the proportion of funds needed to improve engineering safety in the whole project (especially construction projects) is getting lower and lower now, and the supply of materials is also very sufficient. The low safety level in the past only met the needs of the shortage-oriented planned economy era, but it was by no means risk-free. If the safety level of the code is high, some safety accidents that have occurred could have been avoided, and this defect of the code was covered up by the formulation of "three normality" to some extent. The projects under construction must serve the modern society in the future, and the safety must have high standards. Low safety and quality standards will be difficult to be recognized in the future international competition. Even if the safety setting level of structural design can be improved to the same level as that of developed countries, there will still be a gap in structural safety due to the poor overall construction quality.

3. Probabilistic reliability design method of structural design code.

Experts who hold positive opinions on the reliability design method in China's codes believe that this is a major scientific and technological progress. The probability definition of safety degree by reliability method is clearer, more scientific and more reasonable than that by fixed safety factor. Of course, there are still many defects in the probabilistic reliability design method itself, which need to be further revised and improved. On the other hand, people who hold the opposite opinion think that the structural design code is aimed at a variety of complex groups, and the uncertainties and uncertainties that need to be considered in the safety degree are very complicated, so it is impossible to describe or deal with them scientifically with the "probability definition from the perspective of statistical mathematics"; The practice of standardizing the reliability method in China for more than ten years shows that it has not brought obvious effect to the safety of structural design, but has caused some confusion in the concept of safety. For engineers and technicians, the structural safety degree becomes more unpredictable and fuzzy after being expressed by reliability index and false failure probability, and it is not as intuitive and convenient as the safety factor when dealing with the safety problems of specific projects. The reliability method in the current design code is immature and has many fundamental defects. They think that the semi-probability multi-safety factor method is more suitable for the specification, and it does not rule out that the results of reliability analysis can be used as a reference, which should be considered when comprehensively judging the reasonable value of safety factors.

Second, the durability of civil structural engineering

The durability of civil structural engineering is related to the service life of the engineering, that is, the ability of the structure to maintain normal functions during the service life. This normal function includes the safety of the structure and the applicability of the structure, which is more reflected in the applicability.

1, Durability of civil structural engineering

Most civil structures are made of concrete. The durability of concrete structure is a worldwide problem that puzzles civil infrastructure projects at present, which is not unique to China, but it has not attracted enough attention from the competent departments of our government and the vast number of design and construction departments.

For a long time, people have always thought that concrete should be a very durable material. It was not until the late 1970s that developed countries gradually discovered that the original infrastructure projects were damaged prematurely in some cases. Concrete infrastructure projects and port projects in many cities in the United States have deteriorated in less than twenty or thirty years or even less; According to a material estimated by the American Civil Engineering Society in 1998, they need 1.3 trillion dollars to deal with the problems existing in domestic infrastructure projects in the United States, and it will cost 80 billion dollars to repair and replace the concrete deck of highway bridges, but now the federal government allocates only 5 billion to 6 billion dollars for this purpose every year. According to the data, highway bridges that need to be restricted due to steel corrosion caused by deicing salt in the United States account for 1/4 of the environmental bridges. Developed countries have invested a lot of research funds in the durability of concrete structures and taken active measures. For example, in Ontario, Canada, in order to cope with the erosion and freeze-thaw damage of snow melting agent, the minimum thickness of concrete protective layer of steel bars gradually increased from 2.5cm in the 1950s to 4cm and 6cm, until 7cm after the 1980s, and the minimum grade of concrete strength also increased from C25 in the 1950s to C40 later. Bridge deck concrete never needs air entraining agent and waterproof layer, and needs to be equipped with advanced waterproof glue membrane and epoxy coated steel bars. However, there is still no clear requirement for durability design of highway bridges in salt-frozen erosion areas in China, and the requirements for concrete cover and strength are only 2.5cm and C25, which are consistent with the above-mentioned Canadian standards in the 1950s.

According to the investigation of the Ministry of Construction in 1980s, most industrial buildings in China need to be overhauled after 25 to 30 years of use, and the service life of buildings in harsh environment is only 15 to 20 years. The use environment of civil buildings and public buildings is relatively good, which can generally be used for more than 50 years, but the service life of outdoor components such as balconies and rain covers is usually only 30 ~ 40 years. The durability of infrastructure projects such as bridges and port projects is more serious. Because the concrete protective layer of steel bars is too thin and the compactness is poor, many projects are corroded and cracks appear in concrete after several years of completion. Generally, after being used for about ten years, the harbor wharf needs to be overhauled due to the cracking and peeling of concrete along the steel bars. Due to spraying deicing salt and icing in winter, urban overpasses in Beijing and Tianjin have problems after more than ten years of use, and some have to be loaded, overhauled or demolished. Salt freezing also caused damage to concrete pavement, and a high-grade highway in Northeast China was eroded in a large area after only one winter. Low-strength C 15 concrete is used as the lining material of railway tunnels in China, which has poor compactness and impermeability, is not resistant to groundwater and locomotive exhaust corrosion, and has serious cracking and leakage. Sampling survey of tunnels under the jurisdiction of several railway bureaus shows that 50.4% of the tunnels are leaking, of which 1/3 is seriously leaking, which leads to the corrosion of accessories such as rails and the leakage of electric traction area, which affects the normal operation. However, the Code for Design of Railway Tunnels issued by 1999 still fails to take appropriate measures for the durability of tunnels, such as appropriately increasing the minimum strength grade of concrete and adding chemical fibers to concrete.

The seriousness and urgency of the durability problem lies in that many of our projects under construction have not learned many painful lessons from the international and domestic, and they are still repeating the same mistakes along the old road. Some newly-built overpasses and expressway bridges in northern cities have not yet taken necessary comprehensive measures from the aspects of material properties and structural structure to prevent freeze-thaw and salt damage. Even for large-scale projects, such as the Lotus Bridge in Zhuhai, which was put into operation in 2000, C30 concrete with 3 ~ 4 cm thick protective layer is still used in the splash zone.

Some experts estimate that the climax of "dry" infrastructure construction in China can last for another 20 years. Due to the neglect of durability, there will be a climax of "overhaul" in 20 years, which may come soon, and its cost will be twice that of these projects.

The reasons that further aggravate the durability problem of concrete structures are:

1) The quality inspection of concrete is customarily based on a single strength index, which leads to improper pursuit of cement strength in the cement industry, increasing the fineness of cement and the proportion of early-strength mineral components, which is not conducive to the durability of concrete. China's cement quality inspection only requires the strength not to be lower than the specified minimum allowable value, while foreign countries also require it not to be higher than the specified maximum value. If the strength exceeds, it is considered unqualified, which is also conducive to the unity of cement product quality.

2) The construction unit improperly speeds up the construction progress, especially the improper intervention of the government administrative leadership on the construction progress. In particular, the durability and quality of concrete need sufficient construction and maintenance period to ensure, and the concept that premature delivery is harmful to life and health also applies to concrete. The so-called projects of building roads, bridges and high-rise buildings in the past few months, and the projects of grabbing work and giving gifts, which are widely publicized by the domestic media, are likely to be short-lived projects and are destined to spend more money on overhaul in the future. Those who complete the construction period stipulated in the contract ahead of schedule will be fined abroad, because this means that the quality of the project may be damaged.

3) Environmental degradation, such as waste gas and acid rain. The area of acid rain in China has exceeded 30% of the national territory.

At present, it is urgent to formulate technical specifications for durability design of infrastructure projects such as bridges, tunnels and port projects as soon as possible, and revise and supplement the requirements of structural durability in the current specifications. The first thing that needs to be clear is the design service life of various infrastructure projects, and the design documents of important projects must include the requirements and demonstration of service life. Many projects under construction still follow the same road in durability. One of the most important reasons is that there is no new basis for engineering designers and construction technicians to follow in durability. More seriously, some provisions in the current code are harmful to durability. In order to improve the durability of concrete, it is an important technical means to reasonably use mineral admixtures such as fly ash and slag in concrete. Some foreign codes even stipulate that admixtures such as fly ash must be added to concrete structures such as bridges, but China's Code for Construction of Railway Concrete Bridges and Tunnels still explicitly prohibits it. In addition, there are still some outdated views in the engineering and technical circles, which have caused resistance to improving the durability of concrete. For example, for fear of affecting the strength of concrete, we don't want to use air entraining agent, which should be used as a conventional means to improve the durability and workability of concrete; For another example, we hope to increase the amount of cement to ensure the strength of concrete, and the lowest amount of cement should have been an important way to improve the crack resistance and durability of concrete.

In the aspect of revising the durability requirements of the code, the Technical Code for Corrosion Protection of Concrete Structures in Hong Kong issued by the Ministry of Communications 200 1 has played a good demonstration role for other civil engineering industries. On the one hand, we should refer to the existing information and experience at home and abroad, and compile the corresponding design and construction technical documents as soon as possible to meet the urgent needs. On the other hand, it is necessary to arrange systematic research projects and increase support for durability research. The durability of concrete structures is one of the most important frontier research fields in the world structural engineering, but China is quite backward in this respect. The durability research of concrete can not be separated from the specific conditions such as raw materials and environment, and needs to consider the characteristics of the country, and can not rely entirely on foreign research results.

Paying attention to the durability of concrete structure is also the need of sustainable development. Raw materials such as cement, sand and stone. The production of concrete needs to consume a lot of land resources and destroy vegetation and riverbed. Carbon dioxide emissions from cement production have accounted for 1/5 ~ 1/6 of the total emissions from human activities, and China ranks second in the world in carbon dioxide emissions. China now produces more than 500 million tons of cement every year, accompanied by more than 2 billion cubic meters of sand and gravel, which is unsustainable in the long run. Extending the service life of the structure means saving materials, and durable concrete should generally be concrete with low cement content and high mineral admixture (industrial waste), so durable concrete meets the needs of environmental protection. The design service life of civil engineering such as bridges and tunnels in the world is mostly 100 years, and some in Britain are 120 years. Considering the huge economic loss and waste of resources caused by insufficient durability, there is a trend to further extend the minimum working life of these projects in recent years. For example, it is proposed that bridges in urban environment should be at least 150 years.

2. Normal detection and maintenance of civil structure engineering in use stage

The concepts of structural durability and service life are inseparable from inspection, maintenance and repair in the use stage, especially for infrastructure projects in the open air and harsh environment. In order to ensure the safety and durability of the structure, some projects should be tested and maintained regularly during the use after completion. There are design specifications and construction specifications for structural engineering in China, but there is no specification on how to use them. Some engineering collapse accidents, such as the recent collapse of Nanmen Bridge in Yibin, Sichuan, are due to the corrosion of the suspenders between the bridge deck structure and the main arch. If there is a requirement for regular inspection, such an accident is likely to be avoided. In some countries, it is compulsory to regularly inspect buildings, bridges, tunnels and other public works whose structural damage may lead to public safety; Even building components such as glass curtain walls and exterior wall tiles are easy to hurt the public after falling, and there is a requirement for mandatory regular inspection. In China, the level of construction management and the quality of accident operators are relatively poor, the quality control and quality assurance system is not perfect, and the standards of structural safety and durability are relatively low. There are many hidden dangers in built projects, so it is necessary to determine the requirements of normal use and regular inspection of civil engineering from the legal system. For the safety and quality of civil structural engineering, although the government has stipulated that the units and individuals responsible for design and construction should be responsible for it for life, the implementation of this regulation lacks maneuverability. To reduce structural safety and quality accidents to a minimum, we should also give priority to prevention and find problems in time through routine testing.

Judging from the state's investment in public engineering construction and the requirements for engineering design, it is necessary to demonstrate the whole life of the project, that is, the whole life expenditure. Only paying attention to the one-time investment expenditure of the project construction and seldom considering the long-term cost of normal maintenance and repair after the completion of the project may not only damage the service life and normal use function of the project, but also be uneconomical to calculate the general ledger economically. In developed countries, maintenance costs are often more important because of the lack of new projects. In Britain, the civil maintenance cost of 1978 rose to 3.7 times that of 1965, and the maintenance cost of 1980 accounted for 2/3 of the total civil expenditure in that year. Although China is a developing country, a large number of projects are being built now, but a large number of projects built in the past have been prematurely aging. 40% of highway bridges in China are over 25 years old. In addition, since the 1990s, the traffic volume has soared, the overload is serious, the previous design standards are low, and the maintenance problems of roads and bridges are very prominent. Because the maintenance cost can not be guaranteed, it will cause hidden dangers of engineering safety, and more overhaul costs will be needed in the future. In terms of civil engineering investment, it is hoped that relevant departments can increase the maintenance cost of completed projects.

In order to speed up the construction of public projects such as roads and bridges, the state now encourages investment companies to invest and give operating income for a certain period of time, such as 30 years as compensation. If there are laws and regulations that require regular inspection and evaluation of important civil works, it can be guaranteed that these works will return to a good functional state in management and operation after a certain period of time. Bridges with a design service life of 1000 can be used normally for at least 70 years, so that the country will not accept a dilapidated project after the expiration of 30 years.

Third, the role and management of technical specifications

This science and technology forum also discussed the positioning, function and management of technical specifications for civil structural engineering, and put forward some views.

For a long time, influenced by the planned economic system, we often regard technical specifications as laws and the specific provisions and requirements of specifications as legal provisions. Technical specifications or regulations, like technical documents such as technical regulations, technical requirements, construction methods and guidelines, are technical standards and have no legal effect in themselves. Only when all parties (owners, design and construction enterprises) agree to take it as the basis of design and construction, and take the contract as the basis, can it be used as the basis of legal arbitration. Legalizing and enforcing technical problems is not conducive to technological progress and creativity, but is easy to become an excuse to shirk responsibility. Of course, from the overall interests of the country and the public, government departments need to put forward the minimum requirements that civil engineering design and construction must meet, and formulate corresponding laws and regulations on major principles such as safety and environmental protection, but laws and regulations generally do not need to provide specific technical ways and methods to achieve these requirements, which is the task of technical standards. The government can also recognize or approve the use of some important technical specifications or some of their contents in principle.

It is not an effective way to solve the recurring engineering accidents by constantly strengthening the compulsion of technical specifications. At present, the relevant authorities have taken out some provisions in the Code for Design of Building Structures, which are clearly listed as mandatory provisions. At the same time, it is stipulated that the design completed by each design unit must be reviewed by the relevant departments or other enterprises and institutions authorized by them. The main content of the review is to control the requirements of mandatory provisions in the specification, and its task is similar to law enforcement; Whether this is wise or not seems debatable. The frequent occurrence of civil engineering accidents in China mainly lies in poor management, especially corruption in management; Secondly, the quality of construction operators is low, which is difficult to solve in a short time; Too much emphasis on the status and role of norms, failure to establish a complete standard system supporting norms, such as the lack of more detailed and specific technical documents such as guidelines and construction methods, can be used to guide and standardize each specific link of design and construction, and there is a certain relationship. From the design point of view, the accident is not mainly due to the failure to comply with the mandatory provisions of the code, but to the wrong scheme or neglect of the main design conditions; There are also some projects that fail because of low design standards, insufficient durability and lack of proper routine tests during use. In fact, it is the easiest to meet the requirements of the mandatory provisions in the design code, so it seems unnecessary to ask professionals to review it. Important engineering design should require a comprehensive audit by professional units, and its main points should also be on the principles of structural scheme, structural method and calculation and analysis. The mandatory provisions extracted from the national Code for Structural Design are inevitably fragmented, and the provisions of individual provisions may not be suitable for the specific characteristics of certain areas and projects, but cause trouble.

China has a vast territory, unbalanced economic development, great disparity in technical strength and different environmental conditions. Objectively speaking, it is required that the specification can give designers more flexibility and less compulsion, so as to solve problems better under the guidance of the specification and according to the characteristics and specific conditions of the project. In short, in terms of norms and standards, we should get rid of the tendency of excessively demanding unity, giving less consideration to individuality and lacking the flexibility of seeking truth from facts left over from the planned economy era. To advocate and encourage provinces and cities to compile local codes, there may be different standards for the safety and durability of the project. For example, Shanghai, Beijing and Guangzhou are higher, and they are treated differently in terms of earthquake resistance and disaster prevention requirements. The more detailed the national norms are, the worse the applicability may become, and the more confusion may be caused; This is especially true for specifications such as geotechnical engineering.

In developed countries, the specifications of civil structural engineering and all kinds of supporting technical standards are mostly compiled and managed by trade associations or professional societies, and the update cycle of specifications is short, unlike what we need 10 years. Societies and associations in China are duplicated and their division of labor is unclear. They are still attached to a government department, and basically only play the role of unofficial spokespersons of government functional departments, far from being independent, dynamic and sound institutions. How to give full play to the role of these institutions in the compilation and management of technical standards is also a problem worthy of discussion. It is suggested that with the deepening of reform, relevant societies and associations should reorganize and merge, strengthen their functions, and gradually become the main body of technical standards compilation and management.

Four. Proposals submitted to relevant government departments for consideration.

In order to improve the safety and durability of civil structural engineering in China, this forum puts forward the following suggestions for consideration by relevant government departments:

1, durability of concrete structures in infrastructure projects such as bridges, tunnels, roads and ports. It has become a major problem that needs to be taken urgently at present. Otherwise, the normal use function and safety of some projects will not be effectively guaranteed, China's modernization and national economy will suffer huge losses, and will bring long-term troubles to production and public life.

It is suggested that the competent departments of civil engineering design standards of the Ministry of Construction, the Ministry of Communications and the Ministry of Railways should focus on the durability requirements of the project, and make it clear that civil engineering design should have minimum service life requirements, and the design documents of important projects should have independent chapters and discussions on normal service life and durability design;

It is suggested that the National Natural Science Foundation can give key support to the basic theory research of concrete engineering durability in the future.

It is suggested that state administration of work safety should provide project funds in the near future to compile relevant laws and regulations.

It is suggested that the Department of Civil Water Conservancy and Architecture of China Institute of Engineering should contact domestic experts in its consulting research project to promote the compilation of guiding technical regulations for durability design of civil structures.

2, the safety of civil engineering in the process of use, there should be regular testing and normal maintenance and repair to ensure. For important civil engineering, there are no laws and regulations in China that require safety inspection. There is a tendency to focus on construction and neglect maintenance in infrastructure investment, which is not conducive to the project life and investment benefits.

It is suggested that important public infrastructure and public buildings such as bridges and tunnels should be subject to mandatory periodic safety inspections during their service life. Therefore, it is necessary to formulate laws and regulations and formulate corresponding technical standards; For the detection and evaluation of civil structural engineering, it is necessary to establish the registration system of employees and the qualification certification and supervision system of employees. The safety diagnosis of all built projects can also be classified into this industry.

It is suggested that the relevant government departments should increase the proportion of engineering maintenance fees in the investment of civil infrastructure projects such as bridges, tunnels and roads as needed.

3. Improve the technical standard system and management system, and give play to the role of societies and associations in the preparation, revision and management of technical standards; Gradually dilute the mandatory provisions of technical specifications; Encourage the preparation of local norms (standards) and enterprise standards that adapt to the differences in environmental geology, economy and technology in different regions, and encourage scientific and technological innovation and technological progress.

4. To reasonably set the safety level of civil engineering structure design, we must consider the risk consequences of engineering failure, the supply of social wealth and resources, and even the intention of the public. With the great changes in China's economic situation, it is necessary to re-examine the safety setting level of the current civil engineering structure design code, and suggest that the competent department organize the demonstration. The risk consequences of traffic civil structures such as bridges are great, and due to the rapid development of traffic flow, vehicle and vehicle speed, it seems that there should be a higher safety reserve than ordinary building structures in the standard value of design load and the safety setting level of bearing capacity. In the aspect of building structure safety setting, it is suggested to further collect different opinions, including the intention of commercial housing consumers. The level of economic development in different regions of China is very different, so it is worth discussing whether it is necessary to treat buildings differently in terms of safety and durability. 5 The experience and problems of adopting reliability design method in China's building structure design code are worth summarizing. Different types of structures have different preconditions and difficulties in adopting reliability methods, so there is no need to force unity. It is suggested that the relevant departments should collect all kinds of opinions, seek truth from facts and be cautious when extending the reliability method to various design specifications, and should not be eager for success.