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THE CHARACTERISTICS AND CURRENT SITUATION OF STEEL STRUCTURE

The steel structure has the characteristics of light weight, high strength, good plasticity and toughness and short construction period, so it is widely used and developed in the construction project. According to incomplete statistics, from 1964 to 1977, there were about 8000 steel warehouse buildings  of different sizes in China, which used steel grid structure, covering an area of 9 00 square meters. There have been 54 high-rise steel structure projects in China.

We all know that the Olympic stadium "bird's nest", which was held in Beijing in 2008, is also made of steel. The steel structure has an obvious weakness - it is prone to corrosion. According to incomplete statistics, the annual economic loss caused by corrosion in China is over 40 billion people, and about 30 percent of the annual output of 90 million tons of steel is consumed by various forms of corrosion. According to incomplete statistics, the reference value of the economic durability of regular maintenance of steel structure houses is generally: 70 years of production occupancy, 50 years of corroded production, and 80 years of non-production occupancy. And reinforced concrete structure (including frame structure, shear wall structure, cylinder structure, a frame shear wall structure, etc.) : production houses for 50 years, the corrosion production buildings for 35 years, non-production buildings for 60 years. It can be seen that the importance of regular maintenance and maintenance after installation of steel structure.

steel warehouse buildings

However, recent surveys have found that some steel users do not know that steel structures need to be maintained and maintained. That severe corrosion, users often find no, make steel structure products appear many unsafe hidden trouble, reduce the steel structure on the use of safety, and even affect the normal use function. It is suggested that the design unit should not only put forward the coating requirements of steel structure, but also put forward the maintenance and maintenance requirements of the steel structure according to its usage. In the introduction to design should be considered in the process of using steel structures in environmental factors, also want to consider the time of use steel structure, fixed number of year, and then determine the types and coating film thickness, to ensure the service life of steel structure, determine the maintenance time and maintenance method, process, etc., to ensure that prolong the service life of steel structure.

Case 1. By observation, the corrosion of steel structure is increasing exponentially every year. In the first year, it was a spot of rust, and then it formed a bubble of rust. After the bubble burst in the second year, it began to corrode in the deep, and then the coating began to fall off with the iron oxide. In the following table, a steel structure workshop was listed in the following table because it was not thoroughly derusted at that time. In l0 years, there was no corrosion protection and maintenance, which caused serious damage to the steel structure.

 

 

Service life

Corrosion situation

Shedding thickness(mm)

The 1st year

Mottled rust

0

The 2nd year

A small amount of oxidized layer of the air bubble is removed.

0.01

The 3rd year

Large sheets of coated oxide flake off.

0.03

The 4th year

Oxide layer fall off

0.07

The 5th year

Oxide layer fall off

0.12

The 6th year

Oxide layer fall off

0.35

The 7th year

Oxide layer fall off

0.6

The 8th year

Oxide layer fall off

0.85

The 9th year

Oxide layer fall off

1.1

The 10th year

Oxide layer fall off

1.52

 

Case 2: a road bridge collapse in South Korea in 1994 killed many people. The bridge was built in 1979, and no weld cracks have been found in many inspections, but a wide range of rust has been found in the fracture surface of the shaft of the bridge. In the United States, there are 600, 000 highway Bridges, half of which need to be repaired because of steel corrosion. This shows how important the long-term protection of large steel structures is.