| As a vital lifeline engineering, bridge project,once destroyed in the strong earthquakes, there will be great difficulties for the emergency management and bridges restoration. Since the performance based seismic design theory was proposed during the early of 1990's, it has been paid much attention. This new approach gives an economic and rational solution of earthquake resistant strctures.It involves how to decide the nonlinear earthquake demand in a convenient and appropriate way.The dynamic time history analysis is regarded as the most rigorous one,which can trace the course of failure in structures. But it doesn't be used in daily engineering broadly in that there are some inherent restrictions in it,such as,the choice of earthquake waves,huge computation effort,etc.So in a long period of time,the researchers have been trying to seek a convenient method for the solving of nonlinear earthquake demand.Based on the achievement of previous researches, this dissertation focused on the pushover analysis method, the capacity spectrum method and the seismic damage analysis. The paper proposed several improved methods and verified them by simulations. The paper also discussed the application of pushover analysis method on the seismic damage performance design. And an evaluation method of seismic capacity of bridge structures is developed based on the simplified capacity stectrum method. And the effects of the higher modes on response of high pier bridge in different earthquake levels and different space types were discussed.The main contents of this dissertation include:1. The basic principle and procedure of pushover analysis method were studied. The recent applications and the developments of pushover analysis were concisely remarked. Several level loading methods and applied methods of pushover analysis to the bridge seismic performance evaluation and design were dicussed by emphasis.2. Based on the simplified N2 method and the simplified capacity stectrum method,the improved multi-mode capacity stectrum method was porposed in this paper.lt was suitable for the irregular firder bridge with long matural period.3. Seismic damage models are studied from both member level and system level. The principle is discussed for determining the grades of seismic damage of structures, and the relationship is recommended between the damage index and the seismic damage grades of the structure for bridges.4. The principles of establishing the inelastic spectrum by means of force reduction factor R and ductility factorμare elaborated. The inelastic dmand spectra are established according to the new code for seismic design of railway engineering and specifications of earthquake resistant design for highway engineering, and this lays the groundwork for structural inelastic analysis by applying capacity spectra method on the basis of new seismic design code. The influences on demand spectra by different R-μrelationships are also compared in this paper.5. How to choose seismic damage models was studied.A simplified method based on pushover analysis to determine the patameters of seismic damage model and to provide its formulas for calculating was proposed.The effects of the higher modes on response of high pier bridge in different earthquake levels and different space types were discussed. |
