How to correctly choose steel for steel structure

There are many types of steels and properties vary greatly, but the steel suitable for steel structures is only a small part of them. How to correctly select the right steel grade is a very important issue for the steel structure industry, which is related to cost, price, quality, service life and other important links. Xirong steel structure construction into Sichuan steel structure market for 16 years, long-term engineering construction allows us to accumulate a lot of steel selection above practical experience, for this we summarize our experience, while learning from the methods of Chengdu steel structure peers to summarize the following points:

First, the selection principle of steel

The selection of steel should not only ensure the safety and reliability of the structure, but also be economical and reasonable. In order to ensure the bearing capacity of the load-bearing structure and prevent brittle failure under certain conditions, the appropriate grade and quality grade of steel should be selected according to the comprehensive consideration of factors such as the importance of the structure, load characteristics, connection methods, working environment, stress state and steel thickness. Specifically, the following requirements should be met:

1. The importance of structure or components

The corresponding steel grade is selected according to the importance and safety level of the building structure. For important structures such as heavy industrial building structures, long-span structures, high-rise or super-high-rise civil buildings, good quality steel should be selected.

2. Load characteristics

According to the nature of the load, select the appropriate steel, including static or dynamic, regular or accidental, full load or unloaded, etc., and propose the necessary quality assurance measures accordingly.

3. Connection method

There

are two connection methods of steel structure: welded and non-welded. Due to the welding process, welding deformation, welding stress and other welding defects will occur, which may lead to cracks or brittle fractures of the structure, so the material requirements for welding connections are stricter. Compared with the structure of non-welded connections, the content of carbon, sulfur, phosphorus and other harmful chemical elements of the steel used in welding connections should be low, the plasticity and toughness indicators should be high, and the welding performance should be good.

4. Working conditions of the structure

Steel is prone to cold brittleness when it is at low temperatures, so the structure working under low temperature conditions, especially the welded structure, should be selected with calm steel with good low temperature brittleness resistance. Open-air structure is easy to produce aging, and steel acting on harmful media is easy to corrode, fatigue and fracture, and should also be distinguished.

5. Steel thickness

Thick steel not only has less strength, but also has poor plasticity, impact toughness and welding performance. Therefore, the welded structure using steel with a large thickness should use steel with better material.

Second, the basic provisions of steel structure design specifications

1. The steel of the load-bearing structure should use Q235 steel, Q345 steel,

Q390 steel and Q420 steel, and when other grades of steel are used, it should meet the provisions and requirements of the corresponding relevant standards.

2. The load-bearing structure and components in the following situations should not use Q235 boiling steel.

For welded structures:

A. Structures that directly bear dynamic or vibration loads and need to be tested for fatigue;

B. Structures that directly bear dynamic or vibration loads but can not be calculated when the working temperature is lower than -20 °C, and important load-bearing structures that bear bending and tensile under static loads;

C. All load-bearing structures with working temperature equal to or lower than -30 °C.

For non-welded structures: structures with operating temperatures equal to or below -20°C that are directly subjected to dynamic loads and require fatigue verification.

3. The quality of steel should meet the following requirements:

A. The steel used in the load-bearing structure should have the qualified guarantee of tensile strength, elongation, yield strength and sulfur and phosphorus content, and the welded structure should also have the qualified guarantee of carbon content.

B. The

steel used in welded load-bearing structures and important non-welded load-bearing structures should also have the qualification guarantee of cold bending test.

C. For the steel of the welded structure that needs to be tested for fatigue, it should have the qualification guarantee of impact toughness at room temperature. When the working temperature of the structure is not higher than 0 °C but higher than -20 °C, Q235 steel and Q345 steel should have a qualified guarantee of 0 °C impact toughness; Q390 steel and Q420 steel should have a qualified guarantee of -20°C impact toughness. When the working temperature of the structure is not higher than -20 °C, Q235 steel and Q345 steel should have a qualified guarantee of -20 °C impact toughness; Q390 steel and Q420 steel should have a qualified guarantee of impact toughness of -40 °C.

For non-welded structures that need to be tested for fatigue, steel should also have the guarantee of impact toughness at room temperature. When the working temperature of the structure is not higher than -20 °C, Q235 steel and Q345 steel should have a qualified guarantee of 0 °C impact toughness; Q390 steel and Q420 steel should have a qualified guarantee of -20°C impact toughness.

The above is our summary through years of experience, but also refer to the data on many professional books, hoping to help Sichuan steel structure industry peers, and owners with steel structure construction plans. We will summarize and summarize many professional problems of steel structure in the later stage, please continue to pay attention to the construction of Xirong steel structure.