General Design Methods for High-Strength Steel Structures

Compared to ordinary strength steel, high-strength steel involves more complex design

considerations. In addition to the elastoplastic analysis common to ordinary strength steel, greater attention must be paid to

the seismic performance of high-strength steel. This is due to the lower carbon content in high-strength steel,

which, while providing high strength, leads to an increase in the yield-to-tensile ratio of components

and a reduction in the material's plastic deformation capacity. As a result, the elongation of high-strength steel often fails

to meet the design requirements specified in China's "Code for Seismic Design of Buildings." Therefore, in seismic

fortification zones in China, the steel strength used in buildings is typically limited to less than 345 MPa,

which restricts the practical application of high-strength steel. The specific design principles are as follows:

First, the elastic design stage. This stage primarily considers the load-displacement changes that occur when high-strength steel is subjected to elastic forces. Typically, the ultimate bearing capacity is analyzed based on the compressive, bending, and shear strengths of high-strength steel in the elastic stage. Structural bearing capacity verification is then conducted according to its ultimate bearing capacity.

Second, the plastic design stage. This stage mainly analyzes the curve of structural bearing capacity and displacement changes when high-strength steel undergoes plastic deformation. By examining the failure buckling modes of high-strength steel after reaching its ultimate bearing capacity, the instability limit load of high-strength steel is determined. Subsequently, various composite structural forms are selected to combine components with good plastic development capabilities with high-strength steel components, enabling each material to leverage its characteristics. This ensures that the structure maintains good strength, stiffness, and stability in both elastic and plastic states.

Third, the seismic design stage. By analyzing the stress-strain curve of high-strength steel under seismic loads, the post-earthquake deformation and instability of high-strength steel are evaluated. In seismic design, large seismic loads are typically used for pushover analysis of the structure. This requires the structure to not only meet bearing capacity requirements but also satisfy deformation requirements. It is essential to ensure that the deformation caused by seismic loads during an earthquake remains within the specified limits. Components in deformed areas must possess sufficient plastic deformation capacity and the ability to develop plasticity. Combined with reasonable adjustments to the structural form, this enables the structure to effectively dissipate seismic energy and maintain safety and stability under large seismic loads [6].