Studies And Improvements Of Structural Static Elastoplastic Analysis Methodology

Dynamic time history analysis method and static elastoplastic analysis method is by far the most commonly used seismic response analysis methods. Although dynamic time history analysis method is the most accurate seismic response analysis method in earthquake engineering, some key technologies of dynamic time history analysis method, such as imported vibration and the components of the uncertainty of the restoring force model, etc, have not been well solved, and it need to be further researched. Static elastoplastic analysis method which puts forward in order to satisfy the engineering requirement, is a simplified nonlinear seismic response analysis methods. But precisely because it is a kind of simplified calculation method, the equivalent of single degree of freedom and simplifying of pushover curve, static elastoplastic analysis may bring greater error for some structures, so it also need to be further researched and improved.In this paper, firstly, aiming at the problems existing in the ground motion selection method of dynamic time history analysis, the correlation between the spectral value and the nonlinear seismic response of the structure is studied. And it proved that the current commonly used "dual index" ground motion selection method is not applicable to the dynamic time history analysis of structure under the rare earthquake. So "three index" ground motion selection method is proposed in this thesis which use yield period as the wave selection index. Ihen using bottom shear, vertex displacement and maximum displacement between layers of structure as seismic response statistics, It’s Discrete character of two ground motion selection method has being compared. Proved by examples, the "three index" ground motion selection method this thesis proposed greatly reduces the discrete character of seismic response, improved the shortcoming of the original method which would lead to seismic response smaller than requirement, so the structure dynamic time history analysis can guide seismic design and evaluation more effectively.Based on the structure stiffness will degrade and modal parameters will change in plastic state, the single degree of freedom system equivalent method of modal pushover analysis (MPA) is improved on the third chapter of this thesis. A "two stage" equivalent method is proposed, and the steps of the improved MPA method is rearranged. Using three reinforced concrete plane frame as examples, the accuracy of the method is verified through dynamic time history analysis method.For the bilinear simplified method cannot accurately approximate pushover curve with the decline (usually exist in the old buildings), the tri-linear piecewise homenergic approximation method is proposed to fit to the pushover curve of the soften structure. Study indicated that tri-linear simplified line is closer to actual pushover curve of structure which existing soften phenomenon, and it also can predict the yield point and maximum point of structure capacity curve more precise, so it has higher seismic displacement demand precision.