Basic Knowledge of steel structure

Features of steel structure

Selection rules of steel structure

The material selecting principle of steel structure is ensuring the carrying capacity of its bearing structure and preventing brittle failure under certain conditions. The material selection of steel structure is decided according to the importance of the structure, load characteristics, structure types, stress states, connection methods, the thickness of steel, and the working environment.

“Steel Structure Design Code (GBJ)” GB50017-2003 suggests four types of steel which are appropriate in steel structure. Those four types of steel are the first choice under permit conditions but not limited, you can also choose other steels as long as they meet the specs.

Commonly used designations of steel:

Ø  Carbon structural steel: Q195, Q215, Q235(A36/S235), Q255, Q275, etc.

Ø  Low-alloy high-strength structural steel

Ø  Quality carbon structural steel and structural alloy steel

Ø  Special steels

The application of steel structure

Using steel structure is selected not only according to its characteristics but also considered comprehensively according to the specific situation.

In addition to the characteristics of the industry, the application of steel structure must also be considered in combination with specific conditions. The applications of steel structure are as follows:

1, Workshop structure

Workshops with large lifting capacity crane or with heavy work most use steel structure. For example, the open-hearth workshop, blooming workshop and mixer workshop of metallurgical plant and the steel casting workshop, hydraulic press workshop and forging workshop of heavy machinery plant and the berth workshop of the shipyard, the assembly workshop of the aircraft manufacturer, etc. The main load-bearing skeletons of these workshops are usually all or part of steel structures. Recently, more and more general industrial workshops use grid structure with the wide application of steel structures.

2 Long-span structure

It is used in the hall, gymnasium, exhibition hall, theatre, hangar, garage, bridges, etc. The main structural systems adopted are frame structure, arch structure, grid structure, suspension structure and prestressing steel structure.

3 Tower mast structure

Used for tower mast structure such as TV tower, microwave tower, high voltage transmission line tower, chemical exhaust tower, atmospheric monitoring tower, oil drilling tower, rocket launching tower and radio mast, etc.

4 High rise building

The framework of multi-story and high-rise buildings can adopt steel structure. As with multi-story and high-rise or super high-rise buildings in industrial buildings such as hotels, restaurants and so on, the frames should adopt frame structure systems, frame support systems, and frame shear wall systems.

5 Structures subjected to vibration loads or earthquakes

Just like workshops with large forging hammers, the skeleton structure bears extremely strong indirect vibrations although it doesn’t need bearing too much load. Steel structure should also be adopted for structures with high seismic resistance requirements

6, Shell structure

Containers made of steel plates are widely used in metallurgical, petroleum, and chemical enterprises, such as large liquid storage, gas storage, blast furnace, hot blast stove, etc.

7 other structures

Such as trestle, pipe support, derrick, offshore production platform, etc.

8 Removable structure

It is used for assembly movable houses, temporary exhibition halls, etc.

Connection Methods of steel structures

The connection methods of steel structure include welding connection, bolt connection and rivet joint.

1 Welding connection

Welding connection is a process by which the parts that are to be connected are heated and fused, with supplementary molten metal at the joint. Welding connection is the most connection method in modern steel structures.

Advantages:

Ø  It can directly connect any type of components, simple in structure.

Ø  Cost-saving, without weakening the cross-section

Ø  Operating convenient can be automated

Ø  Reliably sealing and high stiffness

Disadvantages:

Ø  The metallographic structure of the steel changes in the heat-affected zone around the weld joint, which causes embrittlement of the material.

Ø  During the welding process, the structure will generate welding residual stress and residual deformation under the influence of the uneven distribution of heating and cooling, which affect its bearing capacity, rigidity and properties.

2 Bolted connection

The bolted connection is a connection method joining the components together by bolts. The bolted connection includes ordinary bolted connections and high-strength bolted connections

Advantages:

Ø  The construction technology is simple

Ø  Convenient to install

Ø  Especially suit field installation

Ø  Easy to take apart and reassemble elsewhere, so it’s suitable for temporary structures

Disadvantages:

Ø  During the assembling process, adjusting holes will increase the manufacturing workload;

Ø  High accuracy required

Ø  The bolt holes weaken the cross-section of structures

Ø  Cost more steel (increasing cost)

3 Riveting connection

The riveting connection includes hot riveting and cold riveting. Hot riveting is the components riveting by riveting gun or squeeze riveter after installing red-hot rivets into the nail holes of the structures.  Cold riveting is that the components riveting at normal temperature and high pressure. Hot rivet is commonly used in building structures.

Due to its complex process, high cost and high labor intensity, rivet connection is rarely used in nowadays. And rivet connection has gradually been replaced by welding connections and bolted connections. Sometimes it’s still used in structures bearing dynamic loading for rivet connection has characteristics of good plasticity, good toughness, reliable force transfer and easy to check.