MPA And Ida-based Performance Evaluation Method For Eccentric Structures

The Performance-Based Earthquake Engineering (PBEE), including the theory and method of design, are issues paid attentions extensively by earthquake engineering academia and engineers at present. The contents of PBEE include the evaluation of the seismic behavior of structures, optimization of the structural performance based on capacity criterions and design of different seismic intensity rationally to reduce possible loss of life and property. The performance of structures should be evaluated accurately and efficiently according to PBEE theory, which is one of the most important subjects in PBEE. On the other hand, there are more and more complicated structures were built up in the cities of China, including many asymmetric and irregular buildings. Estimation of the seismic performance of the asymmetric and irregular buildings has become a key issue in the research of performance analysis at present.The capacity spectrum method adopting single degree of freedom model and considering uni-dimensional ground motions cannot capture the lateral-rotational coupled effect. This work developed multi-degree of freedom systems based on the modal information of asymmetric structures and extended modal pushover analysis method in the performance estimation for asymmetric structures. Fast estimation procedures for the asymmetric structural performance are proposed. The method of performance estimation for asymmetric structures is improved, which provides a new approach to performance-based design for asymmetric structures. The main contents of this dissertation are followed.(1) The capacity curve deduced from multi-mode nonlinear static procedure (NSP) has showed unstable phenomenon in practice. The mechanism of the unstable phenomenon has been analyzed in this work. The result indicated that the unstable phenomenon do not occur in real structural responses and it is caused by higher-modal pushover analysis. By making utility of the equivalent deformation index deduced from the deformation energy of the structures, the unstable issue of the higher modal capacity curve is solved. Compared with the method based on the roof displacement, the new method is stable and possess favorable precision with relatively computational cost. Furthermore, the unstable capacity curve prevented can pave the way for the extension utility of the modal capacity spectrum for asymmetric buildings.(2) One-way asymmetric structural model subjected to uni-directional seismic excitation is common and widely used in the research of asymmetric structures responses. By calculating the rotational capacity curve from the base torque and top rotational angle including the lateral-rotational coupled effect, the modal pushover analysis and capacity spectrum method is extended for asymmetric structures. The Equivalent Dual-Degree of Freedom (EDDOF) system is proposed by offsetting the mass at the top of the SDOF model for construction of the eccentric property. The NSP provides the hysteretic rules for the nonlinear property of EDDOF model, and the coupled effect is considered in NSP. The issue of performance estimation of one-way asymmetric structures including lateral-rotational coupled effect can be solved fast and reliable.(3) The two-way asymmetric structures subjecting dual-directional seismic excitation will generate complicate nonlinear responses. Based on the modal decoupled operation, the problem is simplified by decoupling the responses into lateral responses and rotational response. The Equivalent Triple-Degree of Freedom (ETDOF) model is proposed based on the decoupled modal equations. The performance evaluations issue of two-way asymmetric structures is solved with high precision and efficiency. In addition, the equal displacement rule is adopted to determine the target displacement of NSP, which simplified the procedure and improved the robustness for three dimensional issues.(4) For many NSP methods, the loading distribution takes effect on the performance evaluation results directly. Considering the nonlinear development of the structures, the adaptive load pattern is accepted as the most reasonable formula at present. However, the adaptive load distribution algorithm is with poor stability. Firstly, the study summarizes and discusses different load patterns. By transforming the deformation energy into three equivalent deformation indexes, the stability issue is solved and the adaptive algorithm is improved. The adaptive modal combination procedure (three dimensional capacity spectrum method) is proposed and the method is verified with a complicated asymmetric structure subjecting two-way seismic excitation.(5) The equivalent multi-degree of freedom models present the lateral-rotational coupled effect and can capture the peak deformation responses very well. On the other hand, the Incremental Dynamic Analysis (IDA) can be used in the performance evaluation for many performance criterions. However, IDA is a computationally extremely work. Based on IDA and the equivalent multi-degree of freedom models, the 2D-IDA method and 3D-IDA method are proposed for one-way asymmetric structures subjected to uni-directional excitation and two-way asymmetric structures subjected to dual-directional excitation, respectively. The 2D-IDA and 3D-IDA methods can evaluate the performance overall stages from elastic phase to collapse prevention level for reliability and collapse fragility consideration with computational simplicity.