Basic knowledge of steel structure design: earthquake resistance of steel structure

Steel structures

In the September 1985 earthquake in Mexico (magnitude 8.1), there were 102 steel structures in the high intensity area of Mexico City, of which 59 were built after 1957, and steel buildings built after 1957 collapsed Or the damage is not serious. Compared with the reinforced concrete structure, the steel structure is lighter. Why is the steel structure of the steel structure light earthquake damage? The following editors from China Research and Construction Jianbian take you to decipher the secret of steel structure seismic design in the steel structure.

The seismic design of general steel structures can be briefly described as follows:

1. Perform dynamic analysis to obtain the necessary lateral force. Before the calculation, there must be the most basic structural elements, especially the structure's own weight and lateral force transmission system must have a clear plan. The simplest dynamic analysis is the bottom shear method. This is calculated by calculating the weight and distribution of each floor. More popular is the utility software for linear modal analysis. Modal analysis depends on the self-weight of the structure, the distribution and stiffness of the lateral force elements.

2. Design the lateral force transmission unit. The force obtained from the dynamics needs to be reduced in consideration of the ductility of the lateral force element. The ductility coefficient is specified by the specification. Be careful not to be too conservative in design. As the energy-consuming structure of the entire building, the lateral unit only needs to satisfy the calculation of the lateral force. The reason is that excessive cross sections reduce the ductility of the structure and all other components are affected. After determining the cross section, the actual ductility needs to be calculated. This is because the section actually selected will be larger than the interface required for the calculation. So the actual ductility will be lower than the theoretical ductility.

3. Design the columns and other major components connected to the lateral unit. In order to meet the requirements of a "strong column", the maximum possible lateral element force is used, that is, the ultimate bearing capacity of the lateral element is considered.

4. Design the foundation. The design idea is the same as 3). If the geology is good, such as rocks, you can design at the end.

5. Design partitions. Of course, consider whether it is rigid or semi-rigid. The destruction of the partition will cause brittle failure or collapse of the structure, so the design idea is not to yield, and it must be within the linear range. It involves struts, strings, connection styles; cut connectors, and more.

According to the level of earthquake resistance, it can be divided into several cases.

1. Civil houses in rural areas have the worst earthquake resistance, 90% of which collapsed during the Wenchuan earthquake; followed by multi-layer brick-concrete structures, which are more common in 6 to 10 floors, because of the large amount of bricks and strong brittleness;

2. The bottom frame structure, that is, the bottom layer is a frame structure, which is used as a commercial outlet on the street. The opening is large. The two or more floors are brick-concrete structures. Because the two materials have different rigidities and are light and heavy, the bottom layer easily collapses after an earthquake.

3. Relatively strong and earthquake-resistant is the frame structure, which is more common in buildings with more than 10 floors; the better is the frame shear wall structure, and the better is the pure shear wall structure.

4. Frame shear wall structure. The building of this structure has not been damaged during the Wenchuan earthquake and its performance is very good. According to reports, the shear wall is a concrete structure with high rigidity and strong resistance to horizontal earthquakes.

5. Another kind of strongest is the steel structure, which is mostly used in shopping malls, passenger stations and other buildings. It is also widely used in Japan and other countries. It has good flexibility and can absorb seismic forces, but the cost is very high.

The earthquake resistance of steel structures has been truly tested in many natural and man-made disasters. This is one of the reasons why steel frames are used in many factories and buildings.

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