Theory and design method of seismic design of building structures

Seismic fortification level refers to the magnitude of seismic intensity that may be used in future building structures. Because the seismic fortification level has a direct impact on the seismic performance of building structures, it is necessary to refine the seismic fortification level in the process of seismic mode design of building structures in order to ensure that different levels of seismic fortification level can effectively control the failure state of building structures under different seismic intensities.

The seismic performance level of building structure refers to the maximum damage degree of building under different fortification earthquake levels, including the integrity, adaptability and safety of building structure. According to the study of the actual earthquake disaster, although the buildings designed according to the traditional design concept can avoid the casualties caused by collapse, they can not effectively reduce the huge economic losses caused by the functional loss of basic equipment and components caused by the structural damage of buildings.

Based on the design requirements of seismic mode of building structure, many influencing factors such as non-structural components, structural components, internal equipment, decoration and so on should be considered. It is also necessary to set a detailed and accurate seismic performance grade of building structures to expand the selection range.

The seismic performance target of building structure refers to the expected seismic capacity of building structure according to a certain fortification earthquake level. To establish the seismic performance target of building structures, we must comprehensively consider various influencing factors, such as site characteristics, project investment and benefits, and the potential value of buildings. Among them, according to the importance of the building, the seismic performance targets of the structure are divided into basic fortification targets, important fortification targets and special fortification targets.

Scholars in engineering circles at home and abroad attach great importance to the research of seismic modal design method of building structures based on functional utilization, and generally form a unified view on the objectives and concepts of seismic design. Generally speaking, the seismic design methods of building structures based on functional utilization can be summarized into three types: bearing capacity design method, displacement design method and energy design method.

At present, the bearing capacity design method is often used in the seismic design codes of building structures all over the world. So I won't introduce it in detail, but mainly introduce two design methods.

The displacement design method is to represent the structure as a displacement equivalent single-degree-of-freedom oscillator by replacing the structure method, and to represent the structure by secant stiffness at the maximum displacement and equivalent viscous damping adapted to the hysteretic energy absorbed during inelastic response. Then, by using the predetermined design displacement response spectrum and the damping estimated from the expected ductility, the equivalent period at the maximum displacement can be obtained. Therefore, according to the periodic equation of single-degree-of-freedom oscillator, the effective stiffness at the maximum displacement can be obtained.

Under the action of strong earthquakes, building structures lose energy due to inelastic deformation. Capacity design method refers to effectively controlling the seismic capacity of building structures by controlling the energy consumption capacity of facilities or internal structures. However, due to the influence of structural complexity, the calculation process of hysteretic energy consumption is complicated and the error is large.

Although there are still many defects in the design method and theory of seismic mode of building structures based on functional utilization, it is quite difficult to practice, but the seismic design of building structures based on functional utilization is an inevitable trend of seismic engineering design.