Nonlinear Response Analysis Of Large-Span Complex Structures Under Specially Varying Earthquake Ground Motions

The ground motion is a complicated time-space process. There are some characters about the seismic in the process of propagation, such as incoherence effect, wave-passage effect, site-response effect and attenuation affect etc. It has been verified that the ground motions inputting at different supports of large-span structures are different, which may be modeled by phase shifts and coherency losses. The phase shifts are caused by waves propagating, while the coherency losses can be attributed to many factors such as source mechanism, path and local site effects, etc. Significant contributions on these issues have been made, and studies on response of large span structures have shown that the effects of multi-support excitations must be considered. This thesis will work in the nonlinear response analysis of large-span complex structure under specially varying earthquake ground motions, and the main contents are as following.1. Generation of ground motion fieldIn the response analysis of large-span structures under specially varying earthquake ground motions, series of seismic waves are needed. Although there have been many recordings about seismic, but the sites about the structures are different, and the present seismic recordings are not satisfying the needing of structures analysis. So, response analysis of structure under seismic need generate artificial ground motions. In this thesis, based on the controlling influence of phase-difference spectrum on the non-stationafity of ground motions, and the relationships of the phase spectrum, power density spectrum and flourier amplitude spectrum, the ground motion field is generated. The statistic model of phase-difference generates the phase-difference spectrum, the statistic model of power spectrum generates the power spectrum, and the statistic model of the coherence function considers the coherence character. The generated ground motion field can consider the influences of incoherency effect, wave-passage effect, and local site effect.2. Time-history analysis models of structure under multi-support earthquake excitationsThere are some models in structure analysis under seismic excitations, and it is very difficult to select a rational model used in the time-history analysis. In this thesis, the analysis models of structure under multi-support seismic excitations are studied. When the earthquake occurred, the ground motion inputs at multiple supports of structures are different. Base on the static equilibrium equation of supports offset, the dynamic equilibrium equation of structure under time-varying base movement is derived, and four different analysis models are presented. A frame structure under seismic excitation is studied using these four models.3. Response analysis of large-span structures under multi-support excitationsThe responses of structure under multi-support excitations are influenced by (1) incoherency effect, (2) wave-passage effect, (3) site-response effect, and (4) attenuation effect. It is found that the influence of attenuation effect is small, and can be ignored. In the thesis, the influences of the three effects to structure response under multi-supports excitations are studied. It is including the influence study of single effect, namely as wave passage effect, spatial incoherent effect and site-response effect, and the influence study of two effects assembly and three effects assembly.4. Linear response analysis of national stadium under specially varying earthquake ground motionsThe time history analysis method is applied to analyze the National Stadium. Spatially varying ground motion time histories are simulated for the analysis. The responses of uniform support excitation and multiple support excitations of the National Stadium are studied, in which the spatially varying excitations and uniform excitation in two horizontal and vertical directions are considered.5. Application of substructure for large-span complex structure under multi-supports excitationsSubstructure method is an advanced analytical technique of FEM, and it is of great value and prospects for engineering. The aims for using substructure is to save computing time and to solve super scale problems under limited computing resource. In this thesis, the using of substructure in large-span complex structure for dynamic nonlinear analysis is studied. The fundamental equation is presented and the application process of substructure method is also discussed, A two-floor spatial frame is studied by the substructure method. It proves that the Substructure method is valid and feasible in dynamic analysis.6. Nonlinear response analysis of national stadium under specially varying earthquake ground motionsUnder the strong earthquake, the structure may be into nonlinear, including geometric nonlinearity and material nonlinearity. The nonlinear responses of uniform support excitation and multiple support excitations of the National Stadium are studied, in which the spatially varying excitations and uniform excitation in two horizontal and vertical directions are also considered.