China is a country with many earthquakes, the seismic design of steel structure must be emphasized. The principles of seismic design in this chapter are in accordance with the current national standard "Code for Seismic Design of Buildings", and are applicable to seismic design of steel structures in areas with seismic fortification intensity of 6-9 degrees.

Seismic design includes steel structure of various systems of frame beam, frame column, center support, eccentric support, buckling restraint support, beam-column joints, all kinds of connections, as well as large span roof and other components bearing capacity checking and the corresponding structural requirements.

These artifacts will actually bear the vertical load, but the earthquake under the action of the component to resist lateral force will be the first to reach the limit state, as the earthquake reciprocating, degradation of bearing capacity of these components will, under the vertical force will transfer back to the original adjacent columns, so the beams and pillars on either side of the component to resist lateral force, should according to withstand all the vertical load design.

This article is an important provision to ensure the ductility of the structure and ensure that the structure is carried out in accordance with the predetermined failure path of the steel structure design. The provisions of this section shall apply to basic systems and dual lateral force systems including such basic systems. When not in conformity with the provisions of this article, the structural ductility class ⅴ.

The first clause of the exemption clause is because the second order bending moment will not appear on the top of the top column with the increase of the lateral movement, and the external bending moment will not increase. According to the rules of the plastic yield surface, the axial force does not need to decrease without the increase of the bending moment, so the plastic hinge will be formed on the top of the top column without adverse effects. The second is to ensure that the column has enough bending resistance to resist the second order bending moment with the increase of lateral displacement in the elastic-plastic seismic response process; Further, if the bending resistance of the column is insufficient, the bending moment caused by the vertical load borne by the column can be unloaded because the axial force of the column is impossible to unload. Therefore, the frame beam should be calculated in accordance with the simple supported beam bearing vertical load capacity, can be calculated in accordance with the composite beam section bearing capacity; Meeting article 3 means that this layer is not a weak layer, so the development of lateral movement between layers is limited and there is no need to meet the requirements of strong columns and weak beams. Article 5 The elastic bearing capacity has been improved to basically meet the requirements of moderate earthquake elasticity, so there is no need to meet the requirements of strong columns and weak beams.

For the large span roof structure itself, because of its light weight, good stiffness, the earthquake damage is generally less than other types of structure. The earthquake damage also shows that the support and its adjacent members are more damaged, which is the weak part. The research and steel structure engineering experience show that it is an effective seismic measure to increase the bearing capacity of bars and joints in this area by amplifying the seismic effect.