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Later maintenance plan for steel structure

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Time of issue:2020-06-23
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(Summary description)Chapter 1 Characteristics and current status of steel structure buildings

The steel structure has the characteristics of light weight, high strength, good plasticity and toughness, and short construction period. Therefore, it has been widely used and developed in construction projects. According to incomplete statistics, from 1964 to 1977, about 8000 buildings of different sizes in our country used steel grid structures, with a total coverage area of 900 square meters; high-rise steel structure projects that have been built and are under construction in China There are 54 buildings.

As we all know, the "Bird's Nest" of the Olympic Stadium held in Beijing in 2008 also uses steel structure. The steel structure has an obvious weakness-easy to corrode. According to incomplete statistics, the domestic economic loss caused by corrosion is more than 40 billion people every year, and about 30% of the annual steel production of 90 million tons is consumed by various forms of corrosion. According to incomplete statistics, the reference value of the economic durability of steel structure houses that are regularly maintained is generally 70 years for production houses, 50 years for corroded production houses, and 80 years for non-production houses. Reinforced concrete structure (including frame structure, shear wall structure, cylinder structure, frame-shear wall structure, etc.): 50 years for production houses, 35 years for corroded production houses, and 60 years for non-production houses. It can be seen that the importance of regular maintenance and repair after the installation of the steel structure is completed.

However, investigations in recent years have found that some users of steel structures do not know that steel structures still require maintenance and upkeep. To the extent that there is severe corrosion, users often cannot find it, which makes steel products have many hidden dangers, which reduces the safety of the steel structure and even affects the normal use function. It is recommended that the design unit not only put forward the requirements for the coating of the steel structure, but also put forward the requirements for the maintenance and maintenance of the steel structure according to its use in the design description of the coating of the steel structure. In the design specification, the environmental factors of the steel structure during use should be considered, and the time and years of use of the steel structure should also be considered, and then the type of coating and the thickness of the coating film should be determined to ensure the service life of the steel structure and determine maintenance. The time and maintenance methods, processes, etc., to ensure that the service life of the steel structure is extended.

Case 1, through observation, it is found that the corrosion of the steel structure basically doubles every year at an increasing rate. In the first year, rusty spots were formed, and then rust-point bubbles were formed. In the second year, the bubbles began to corrode in depth under the urging of the external medium, and then the coating began to fall off with iron oxide. The following table lists the annual corrosion status of a steel structure factory due to the incomplete rust removal at that time. The corrosion prevention and maintenance of the steel structure was not carried out once in 10 years.

Case 2: In 1994, a road bridge collapsed in South Korea, causing many deaths. The bridge was built in 1979. Weld cracks were not found in multiple inspections, but a large amount of rust was found on the fracture surface of the bridge's vertical rod. There are 600,000 highway bridges in the United States, half of which need to be repaired due to steel corrosion, which shows how important the long-term protection of large steel structure parts is.

Chapter 2 Steel Structure Maintenance and Maintenance

If the steel structure is exposed to air or humidity for a long time, and there is no protective measures on the surface, the steel structure will be corroded, deformed or stressed, and the structure will be prematurely destroyed. Therefore, if you want to make the steel structure work properly and ensure its expected service life, it is very important to check, maintain and maintain the steel structure regularly. The maintenance and repair of steel structure mainly has the following aspects:

1. Regular anti-rust and anti-corrosion protection

2. Regular fire protection

3. Regular deformation monitoring and maintenance

(In the process of use, the overall verticality of the structure, the bending of the plane and the verticality of the main members, bending deformation, mid-span deflection, stress monitoring and other items)

4. Regular inspection and maintenance of other diseases

Chapter 3 Contents and Methods of Steel Structure Maintenance and Maintenance

(1) Regular antiseptic treatment

The general steel structur

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Later maintenance plan for steel structure

Categories:Other News
Author:
Origin:
Time of issue:2020-06-23
Views:0

Information

Chapter 1 Characteristics and current status of steel structure buildings

The steel structure has the characteristics of light weight, high strength, good plasticity and toughness, and short construction period. Therefore, it has been widely used and developed in construction projects. According to incomplete statistics, from 1964 to 1977, about 8000 buildings of different sizes in our country used steel grid structures, with a total coverage area of 900 square meters; high-rise steel structure projects that have been built and are under construction in China There are 54 buildings.

As we all know, the "Bird's Nest" of the Olympic Stadium held in Beijing in 2008 also uses steel structure. The steel structure has an obvious weakness-easy to corrode. According to incomplete statistics, the domestic economic loss caused by corrosion is more than 40 billion people every year, and about 30% of the annual steel production of 90 million tons is consumed by various forms of corrosion. According to incomplete statistics, the reference value of the economic durability of steel structure houses that are regularly maintained is generally 70 years for production houses, 50 years for corroded production houses, and 80 years for non-production houses. Reinforced concrete structure (including frame structure, shear wall structure, cylinder structure, frame-shear wall structure, etc.): 50 years for production houses, 35 years for corroded production houses, and 60 years for non-production houses. It can be seen that the importance of regular maintenance and repair after the installation of the steel structure is completed.

However, investigations in recent years have found that some users of steel structures do not know that steel structures still require maintenance and upkeep. To the extent that there is severe corrosion, users often cannot find it, which makes steel products have many hidden dangers, which reduces the safety of the steel structure and even affects the normal use function. It is recommended that the design unit not only put forward the requirements for the coating of the steel structure, but also put forward the requirements for the maintenance and maintenance of the steel structure according to its use in the design description of the coating of the steel structure. In the design specification, the environmental factors of the steel structure during use should be considered, and the time and years of use of the steel structure should also be considered, and then the type of coating and the thickness of the coating film should be determined to ensure the service life of the steel structure and determine maintenance. The time and maintenance methods, processes, etc., to ensure that the service life of the steel structure is extended.

Case 1, through observation, it is found that the corrosion of the steel structure basically doubles every year at an increasing rate. In the first year, rusty spots were formed, and then rust-point bubbles were formed. In the second year, the bubbles began to corrode in depth under the urging of the external medium, and then the coating began to fall off with iron oxide. The following table lists the annual corrosion status of a steel structure factory due to the incomplete rust removal at that time. The corrosion prevention and maintenance of the steel structure was not carried out once in 10 years.

Case 2: In 1994, a road bridge collapsed in South Korea, causing many deaths. The bridge was built in 1979. Weld cracks were not found in multiple inspections, but a large amount of rust was found on the fracture surface of the bridge's vertical rod. There are 600,000 highway bridges in the United States, half of which need to be repaired due to steel corrosion, which shows how important the long-term protection of large steel structure parts is.

Chapter 2 Steel Structure Maintenance and Maintenance

If the steel structure is exposed to air or humidity for a long time, and there is no protective measures on the surface, the steel structure will be corroded, deformed or stressed, and the structure will be prematurely destroyed. Therefore, if you want to make the steel structure work properly and ensure its expected service life, it is very important to check, maintain and maintain the steel structure regularly. The maintenance and repair of steel structure mainly has the following aspects:

1. Regular anti-rust and anti-corrosion protection

2. Regular fire protection

3. Regular deformation monitoring and maintenance

(In the process of use, the overall verticality of the structure, the bending of the plane and the verticality of the main members, bending deformation, mid-span deflection, stress monitoring and other items)

4. Regular inspection and maintenance of other diseases

Chapter 3 Contents and Methods of Steel Structure Maintenance and Maintenance

(1) Regular antiseptic treatment

The general steel structure has a design life of 50 years, and the chance of being damaged due to excessive load during the use of the steel structure is very small. Most steel structure damage is caused by the reduction of structural mechanical properties and physical properties caused by corrosion. The "Steel Structure Design Code" has certain requirements for the corrosion of steel structures that have been used for more than 25 years. Therefore, it is required that the coating protection on the outside of the steel structure should meet the use requirements of the steel structure. In general, the steel structure needs to be maintained for 3 years (clean up the dust, rust and other dirt in the steel structure and then paint). The types and specifications of the paints should be the same as the original paints, otherwise the incompatibility of the two paints will bring greater harm, and the users should do regular and regular maintenance and maintenance.

1. Methods to prevent the steel structure from rusting

There are many ways to prevent the steel structure from rusting, and the following are usually adopted.

1.1. The steel structure is made of alloy steel that is not easy to rust

1.2, chemical oxide layer protection method

1.3, using metal plating protection method

1.4 Non-metallic coating protection law

In the later maintenance and repair process, the non-metallic coating protection method is particularly commonly used. The surface of the component is protected by paint and plastic so as not to contact with the surrounding corrosive medium, so as to achieve the purpose of anti-corrosion. This method has good effect, low price, and a wide range of coatings. It has a wide range of choices and strong applicability. It is not limited by the shape and size of the component. It can form a film with any shape on the surface of the component. It adheres firmly. It is easy to use because it expands and contracts. It is also possible to give the components beautiful colors.

2. Requirements for daily maintenance of coating

For maintenance personnel, the daily maintenance of the steel structure should first be the maintenance of the surface coating of the component. The maintenance of the coating directly affects the service life of the steel structure. Therefore, to do routine maintenance, you should start with the following points:

(1) The surface of the steel structure must be kept clean and dry, and the places where the steel structure is easy to accumulate dust (such as steel column feet and node plates) should be cleaned regularly.

(2) Regularly check the intact condition of the protective coating of the steel structure. Any one of the following should be maintained in time:

1). It is found that the area of the coating surface tarnished reaches 90%;

2) The area of the coating surface is rough, weathered and dry cracked up to 25%;

3) The paint film is raised on the coating and the area of the member with slight corrosion reaches 40%;

(3) The steel structure parts affected by high temperature and high temperature should be provided with protective plates to protect the coating from high temperature damage.

(4) Try to avoid contact between components and corrosive substances, and those that have been in contact should be cleaned up in time.

3. Repair and update of the coating

3.1 Derusting of component surface

For the steel structure project that has been used for a period of time, there are inevitably some attachments on the surface, such as rust, dirt, dust; old paint film, etc. Before painting the surface of the steel structure, if these attachments are not completely removed, although they can be temporarily covered after painting, because they play a role of isolation, the adhesion between the coating and the component substrate If it drops seriously, the paint film will fall off prematurely, which will eventually reduce the anti-corrosion ability of the surface coating and fail to exert the protective effect that the coating should have. Therefore, before painting the surface of the component, the attachments on the surface of the steel structure should be thoroughly cleaned.

In the construction of steel structure maintenance works, surface cleaning mainly includes removing old paint films. In the process of derusting, due to the constraints of construction conditions, the methods generally adopted are:

1. Manual rust removal

In this method, scrapers, spatulas, hand hammers, wire brushes and other steel products are used to remove dirt by manually knocking the shovel, and manually grinding with emery cloth, sandpaper and grinding wheels, so that the surface of the component is basically free of oil and dirt. Rust and no burrs. This method is convenient and easy to implement, requires simple equipment, low labor cost, and is not limited by the size of the construction site conditions. It is a rust removal method often used in steel structure maintenance projects. Its main disadvantages are poor working conditions, low working efficiency, incomplete rust removal, and poor quality assurance. Therefore, when Han adopts this method to remove rust, managers should emphasize the quality requirements.

2. Mechanical rust removal

In order to improve the rust removal quality and work efficiency. To improve the working conditions of construction personnel, a large number of air-driven or electric small-scale equipment have been used in the current steel structure derusting work. The main rust removal methods using equipment are:

(1) Angle grinder: This small pneumatic device is mainly used for cleaning flat areas. It can use sandpaper, grinding wheels and wire brushes as needed.

(2) Needle beam derusting machine: This small pneumatic device is generally equipped with 30 to 40 needle beams. The needle beams can be adjusted according to different working surfaces. It is mainly suitable for bending, narrow, uneven, and nip.

(3) Single-head cold air gun: This small pneumatic device is also called zinc knocking. It uses the impact of knocking the shovel head to remove rust. The diameter of the shovel head is generally 25~40mm, and it can impact 1000~6000 times per minute. Suitable for relatively narrow places.

3. Sand blasting

In projects that can be shut down for construction and maintenance, sandblasting can be used to remove rust. The rust on the sky surface of the steel structural member is cleaned by a sand blasting machine to reveal the true color of the metal. A better sand blasting machine can automatically screen out the fine powder of the yellow sand, iron sand or iron pellets, and prevent the dust from flying, reducing the impact on the operator's health. This method removes rust thoroughly. The efficiency is also higher, which is widely used in developed countries and is a more advanced rust removal method.

4. Use pickling paste to remove rust

A special descaling pickling paste is available on the market. The method is to apply the pickling paste to the surface of the component underneath. Its thickness is about 1~2mm. After a suitable time of dipping and rolling, peel off a small piece of acid Check the derusting condition by washing the paste. If the metal color is exposed on the surface of the component, peel off the pickling paste and rinse it with water to completely remove the remaining acid. Except for some special cases, this method of rust removal has been rarely used.

3.2 Cleaning of the old paint mold on the surface of the component

For the cleaning of the old paint mold on the surface of the component, different measures can be taken according to the different conditions of the paint film. Specific measures are:

1. If the old paint film is firm and complete, and the surface of the component is well adhered, use soapy water or dilute alkaline water

Remove impurities from the surface of the old paint film, rinse with water and wipe dry, and then apply paint after polishing.

2. If most of the old paint film is well attached to the component, if it needs to be removed locally, divide by the top

In addition to the cleaning method, it should also go through the processes of putty, sanding, paint repair, etc., and strive to make the place flat with the old paint film and the same color.

3. If most of the old paint film has been damaged and peeled off, it must be completely removed. The removal methods are as follows:

1) Fire spraying method: after the paint film is burnt with the flame of a blowtorch, it is immediately scraped off with a spatula. This method is generally used for cleaning small areas of old paint film.

2) Alkaline water cleaning method: dilute solution made of lime and soda ash or 5%~10% (mass fraction) sodium hydroxide solution, brush 3~4 times. Wrinkle and peel off the old paint film, then scrape it off with a spatula and wash it with clean water.

3) Brush paint remover method: apply the paint remover available on the old paint film, about half an hour later, the old paint film expands and wrinkles, use a spatula, wire brush to remove the old paint film clean, remove components Other debris on the surface.

4) Paint stripping paste method: apply paint stripping paste to the surface of the old paint film and apply 2~3 layers for about 2~3 hours. The paint film is damaged. After removing with a spatula, rinse with water. If the old paint film is too thick, in order to shorten the soaking time, you can use a knife to break the old paint film to a suitable number of openings before applying paint stripping paste.

4. Methods and precautions for painting construction

(1) The method of painting construction:

There are two commonly used methods in maintenance engineering, namely brushing method and spraying method.

(2) Matters needing attention:

1) Thoroughly clean the base layer before painting, and keep it dry.

After 8h, apply the primer as soon as possible.

2) When painting the primer, the appropriate painting method should be selected according to the size of the area.

3) When applying topcoat, follow the color and variety requirements of the design

Brushing, the brushing method is the same as the primer brushing method.

4) Paint the environment

5) The thinner should be used correctly.

About common defects, causes and prevention methods in painting construction

(2) Regular fire protection

The temperature resistance of steel is poor, and many of its properties change with the temperature rise and fall. When the temperature reaches 430-540 ℃, the yield point, tensile strength and elastic modulus of the steel will drop sharply and lose the bearing capacity. The steel structure must be maintained with refractory materials. No fireproof paint or fireproof paint was used before. The fire resistance of a building depends on the fire resistance of the building components. When the fire occurs, its carrying capacity should last for a certain period of time, so that people can safely evacuate, rescue materials and put out the fire.

The fire prevention measures are as follows: Therefore, the exposed steel components are to be coated with fire retardant paint. The specific requirements are: the fire resistance time of the steel beam is 1.5h, and the fire resistance time of the steel column is 2.5h, so that it meets the requirements of the building code.

(3) Regular monitoring

The damage of the steel structure to the component not only appears as a reduction in the effective cross-section of the component, but also as a "rust pit" on the surface of the component. The former reduces the bearing capacity of components, resulting in a decrease in the overall bearing capacity of the steel structure, especially for thin-walled steel and light-weight steel structures. The latter makes the steel structure produce "stress concentration" phenomenon. When the steel structure is under impact load or alternating load, brittle fracture may occur suddenly. There is no sign of deformation when this phenomenon occurs, and it is not easy to detect and prevent in advance. For this reason, it is very important to monitor stress, deformation and cracks on steel structures and main components.

1. The main factors causing excessive deformation of the steel structure

(1) The actual dynamic load on the steel structure exceeds the maximum load allowed during the design of the steel structure (commonly known as "overload").

(2) Long-term impact with dynamic load.

(3) The impact of natural disasters (such as earthquakes) or due to uneven foundation settlement.

(4) Improper use and maintenance or mechanical damage caused the components in the steel structure project to break and withdraw from work, resulting in abnormal deformation of the steel structure due to unbalanced forces.

2. Inspection and treatment of steel structure engineering deformation

If the steel structure is deformed too much during the use phase, it indicates that the load-bearing capacity or stability of the steel structure can no longer meet the needs of use. At this time, the owner should pay enough attention to quickly organize relevant industry professionals to analyze the causes of deformation. Put forward the treatment plan and implement it immediately to prevent greater damage to the steel structure project.

(1) Inspection method

When inspecting the deformation of the steel structure project, it is generally first to visually inspect the whole structure and components of the steel structure project for abnormal deformation phenomena, such as excessive bending deformation of the elongated rods and webs. The connecting plate is distorted and deformed. For components that are abnormally deformed by visual inspection, make one more step

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