Theoretical Study On Dynamic Stability And Collapse Prevention Design Of Single-Story Steel Frames

Steel frame structures are more and more widely applied to practical engineering due to their many merits, such as high strength, good plasticity and tenacity, low weight and good aseismic performance. The importance and application in practical engineering of steel frame structures prompt the development of theoretical and experimental research. At present, static stability theories and design methods of steel frames have trends to maturity, but it is lack of dynamic stability research on steel frames, and there is little development to corresponding theory and experimental research. Therefore, it has importantly theoretical and practical value to study dynamic stability and establish anti-collapse design advice of steel frame structures. This paper studies mostly dynamic stability of single-story steel frame structures under different earthquake action. The main research contents are stated as follows: Part 1. According to different axial compression ratio and slenderness ratio, this paper designs 12 types of square section column and 12 types of I section column single-story steel frame structures, and gives overall dimensions and characteristic parameters, then provides data for establishing ANSYS finite element models. According to static equivalent principle, single-story steel frame structure is simplified to semi-column model, and it is proved that the top displacement of semi-column model is a half that of frame. Frame models and semi-column models are established by dimension. Nonlinear static analysis to single-story steel frame structure and semi-column model is analyzed by ANSYS program. Consequently, it is proved that simplified method is correct. Part 2. Fist, dynamic stability analysis of single-story steel frames is analyzed by NONLIN (a software applied to single degree of freedom system). It is convenient in determination of critical accelerations of frame dynamic instability considering P-delta effects. It can provide referenced peak acceleration of earthquake wave for the following dynamic stability analysis of single-story steel frames by ANSYS program. Then, transient analysis method and APDL parameter design language are introduced. According to critical accelerations acquired by NONLIN, earthquake acceleration is adjusted and is input by compiled orders with APDL parameter design language. By dynamic stability analysis to 12 types of square section column frames, it is found that time history curves of displacement, phase-plane trajectory curves, hysteretic curves of restoring force, time history curves of energy of frames at stability and instability are consistent. Moreover, the instable ultimate displacement is basically close. Therefore, the conclusion is acquired that effect of different earthquake waves to dynamic stability of frames is little, that is, ultimate displacement of frame is independent of dynamic load type. Part 3. Nonlinear static analysis of I section column single-story steel frames is studied by ANSYS finite element method. It is found that framework curves of horizontal force and displacement accord with that calculated by modified stiffness and cross-section plastic moment theory. Results show further bilinear horizontal force and displacement model of modified cross-section plastic moment accords with practical framework curve of single-story steel frame. Then, by the dynamic stability analysis to 12 types of I section column frames, the same conclusion with Part 2 is obtained, namely, dynamic stability of frames for both square section and I section is independent of dynamic load type. Part 4. Fist, according to achievements above, it is summarized that the influence of key parameters on dynamic stability of frame, relationship of peak acceleration of earthquake wave and axial compression ratio is given. Then, the range of instable peak acceleration of earthquake wave can be estimated. Furthermore, several methods how to determine structural ultimate displacement are discussed. By research on ultimate displacement combined with code for seismic design and general calculating methods in practical engineering, anti-collapse design advice to single-story steel frames in practical engineering is put forward, this provides the foundation for aseismic design of single-story steel frames.